diff --git a/Documentation/ITK5MigrationGuide.md b/Documentation/ITK5MigrationGuide.md
index 92f5b1d47f1..f30c907f356 100644
--- a/Documentation/ITK5MigrationGuide.md
+++ b/Documentation/ITK5MigrationGuide.md
@@ -405,6 +405,8 @@ Class changes
 [itk::FilterWatcher](../Modules/Core/TestKernel/include/itkFilterWatcher.h) was deleted.
 It should be replaced by [itk::SimpleFilterWatcher](../Modules/Core/Common/include/itkSimpleFilterWatcher.h).
 
+`itksys::hash_map` has been removed. It should be replaced by `std::unordered_map`.
+
 Since `itk::ProgressReporter` does not work well with the new threading model,
 it should be replaced by `itk::ProgressTransformer`.
 This only applies to classes which use `GenerateData()` method, and either
diff --git a/Modules/Core/Common/include/itkEquivalencyTable.h b/Modules/Core/Common/include/itkEquivalencyTable.h
index aa056ed04e6..ea1ab2764f4 100644
--- a/Modules/Core/Common/include/itkEquivalencyTable.h
+++ b/Modules/Core/Common/include/itkEquivalencyTable.h
@@ -20,7 +20,7 @@
 
 
 #include "itkProcessObject.h"
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 
 namespace itk
 {
@@ -55,8 +55,8 @@ class ITKCommon_EXPORT EquivalencyTable:public DataObject
   itkTypeMacro(EquivalencyTable, DataObject);
 
   /** Define the container type for the table. */
-  using HashTableType = itksys::hash_map< unsigned long, unsigned long,
-    itksys::hash< unsigned long > >;
+  using HashTableType = std::unordered_map< unsigned long, unsigned long,
+    std::hash< unsigned long > >;
 
   using Iterator = HashTableType::iterator;
   using ConstIterator = HashTableType::const_iterator;
diff --git a/Modules/Core/Common/test/itkHashTableTest.cxx b/Modules/Core/Common/test/itkHashTableTest.cxx
index 7e2bd45f2e3..693eb682314 100644
--- a/Modules/Core/Common/test/itkHashTableTest.cxx
+++ b/Modules/Core/Common/test/itkHashTableTest.cxx
@@ -16,8 +16,8 @@
  *
  *=========================================================================*/
 
-#include "itksys/hash_set.hxx"
-#include "itksys/hash_map.hxx"
+#include <unordered_set>
+#include <unordered_map>
 #include <iostream>
 #include <cstring>
 
@@ -37,10 +37,10 @@ struct eqstr
   }
 };
 
-void lookup(const itksys::hash_set<const char*, itksys::hash<const char*>, eqstr>& Set,
+void lookup(const std::unordered_set<const char*, std::hash<const char*>, eqstr>& Set,
             const char* word)
 {
-  itksys::hash_set<const char*, itksys::hash<const char*>, eqstr>::const_iterator it
+  std::unordered_set<const char*, std::hash<const char*>, eqstr>::const_iterator it
     = Set.find(word);
   std::cout << word << ": "
        << (it != Set.end() ? "present" : "not present")
@@ -52,19 +52,19 @@ inline void println(const char *s)
 
 int itkHashTableTest(int, char* [] )
 {
-  println("Testing itksys::hash");
-  itksys::hash<const char*> H;
+  println("Testing std::hash");
+  std::hash<const char*> H;
   std::cout << "foo -> " << H("foo") << std::endl;
   std::cout << "bar -> " << H("bar") << std::endl;
-  itksys::hash<int> H1;
+  std::hash<int> H1;
   std::cout << "1 -> " << H1(1) << std::endl;
   std::cout << "234 -> " << H1(234) << std::endl;
-  itksys::hash<char> H2;
+  std::hash<char> H2;
   std::cout << "a -> " << H2('a') << std::endl;
   std::cout << "Z -> " << H2('Z') << std::endl;
 
-  println("Testing itksys::hash_set");
-  using HashSetType = itksys::hash_set<const char*, itksys::hash<const char*>, eqstr>;
+  println("Testing std::unordered_set");
+  using HashSetType = std::unordered_set<const char*, std::hash<const char*>, eqstr>;
   HashSetType Set;
   Set.insert("kiwi");
   Set.insert("plum");
@@ -85,7 +85,7 @@ int itkHashTableTest(int, char* [] )
   // This is to prevent the user from calling empty() when they mean clear().
   if (Set.empty()) std::cout << "Set is empty." << std::endl;
   Set.bucket_count();
-  Set.resize(50);
+  Set.rehash(50);
   Set.insert("the horror");
   Set.count("apple");
   Set.find("kiwi");
@@ -95,8 +95,8 @@ int itkHashTableTest(int, char* [] )
   HashSetType SetCopy;
   SetCopy = Set;
 
-  println("Testing itksys::hash_map");
-  using HashMapType = itksys::hash_map<const char*, int, itksys::hash<const char*>, eqstr>;
+  println("Testing std::unordered_map");
+  using HashMapType = std::unordered_map<const char*, int, std::hash<const char*>, eqstr>;
 
   HashMapType months;
   months["january"] = 31;
@@ -125,7 +125,7 @@ int itkHashTableTest(int, char* [] )
   // This is to prevent the user from calling empty() when they mean clear().
   if (months.empty()) std::cout << "Set is empty." << std::endl;
   months.bucket_count();
-  months.resize(50);
+  months.rehash(50);
   HashMapType::value_type p("psychotic break", 2);
   months.insert(p);
   months.count("january");
diff --git a/Modules/Core/Mesh/include/itkAutomaticTopologyMeshSource.h b/Modules/Core/Mesh/include/itkAutomaticTopologyMeshSource.h
index d7fa6f744b2..67f871a0b66 100644
--- a/Modules/Core/Mesh/include/itkAutomaticTopologyMeshSource.h
+++ b/Modules/Core/Mesh/include/itkAutomaticTopologyMeshSource.h
@@ -20,7 +20,7 @@
 
 #include "itkArray.h"
 #include "itkDefaultStaticMeshTraits.h"
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 #include "itkHexahedronCell.h"
 #include "itkIntTypes.h"
 #include "itkMesh.h"
@@ -145,7 +145,7 @@ class ITK_TEMPLATE_EXPORT AutomaticTopologyMeshSource:public MeshSource< TOutput
 
   /** hash_map type alias. */
 
-  using PointHashMap = itksys::hash_map<
+  using PointHashMap = std::unordered_map<
     PointType,
     IdentifierType,
     StructHashFunction< PointHashType > >;
@@ -388,7 +388,7 @@ class ITK_TEMPLATE_EXPORT AutomaticTopologyMeshSource:public MeshSource< TOutput
                           // are controlled manually
 
 private:
-  using CellHashMap = itksys::hash_map<
+  using CellHashMap = std::unordered_map<
     Array< IdentifierType >,
     IdentifierType,
     IdentifierArrayHashFunction,
diff --git a/Modules/Filtering/ImageStatistics/include/itkAdaptiveEqualizationHistogram.h b/Modules/Filtering/ImageStatistics/include/itkAdaptiveEqualizationHistogram.h
index a3cff31b997..0ae888b6a5f 100644
--- a/Modules/Filtering/ImageStatistics/include/itkAdaptiveEqualizationHistogram.h
+++ b/Modules/Filtering/ImageStatistics/include/itkAdaptiveEqualizationHistogram.h
@@ -18,7 +18,7 @@
 #ifndef itkAdaptiveEqualizationHistogram_h
 #define itkAdaptiveEqualizationHistogram_h
 
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 #include "itkStructHashFunction.h"
 #include "itkMath.h"
 #include <cmath>
@@ -122,7 +122,7 @@ class AdaptiveEqualizationHistogram
   }
 
 private:
-  using MapType = typename itksys::hash_map< TInputPixel,
+  using MapType = typename std::unordered_map< TInputPixel,
                                      size_t,
                                      StructHashFunction< TInputPixel > >;
 
diff --git a/Modules/Filtering/ImageStatistics/include/itkLabelOverlapMeasuresImageFilter.h b/Modules/Filtering/ImageStatistics/include/itkLabelOverlapMeasuresImageFilter.h
index a3b7a8d99bd..95f56c9d040 100644
--- a/Modules/Filtering/ImageStatistics/include/itkLabelOverlapMeasuresImageFilter.h
+++ b/Modules/Filtering/ImageStatistics/include/itkLabelOverlapMeasuresImageFilter.h
@@ -21,7 +21,7 @@
 #include "itkImageToImageFilter.h"
 #include "itkNumericTraits.h"
 
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 
 namespace itk {
 
@@ -116,7 +116,7 @@ class ITK_TEMPLATE_EXPORT LabelOverlapMeasuresImageFilter :
     };
 
   /** Type of the map used to store data per label */
-  using MapType = itksys::hash_map<LabelType, LabelSetMeasures>;
+  using MapType = std::unordered_map<LabelType, LabelSetMeasures>;
   using MapIterator = typename MapType::iterator;
   using MapConstIterator = typename MapType::const_iterator;
 
diff --git a/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilter.h b/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilter.h
index ebe873fb7a2..8489501c9be 100644
--- a/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilter.h
+++ b/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilter.h
@@ -23,7 +23,7 @@
 
 #include "itkConceptChecking.h"
 
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 
 namespace itk {
 /** \class LaplacianDeformationQuadEdgeMeshFilter
@@ -180,11 +180,11 @@ class ITK_TEMPLATE_EXPORT LaplacianDeformationQuadEdgeMeshFilter:
   LaplacianDeformationQuadEdgeMeshFilter();
   ~LaplacianDeformationQuadEdgeMeshFilter() override = default;
 
-  using OutputMapPointIdentifier = itksys::hash_map< OutputPointIdentifier, OutputPointIdentifier >;
+  using OutputMapPointIdentifier = std::unordered_map< OutputPointIdentifier, OutputPointIdentifier >;
   using OutputMapPointIdentifierIterator = typename OutputMapPointIdentifier::iterator;
   using OutputMapPointIdentifierConstIterator = typename OutputMapPointIdentifier::const_iterator;
 
-  using ConstraintMapType = itksys::hash_map< OutputPointIdentifier, OutputVectorType >;
+  using ConstraintMapType = std::unordered_map< OutputPointIdentifier, OutputVectorType >;
   using ConstraintMapConstIterator = typename ConstraintMapType::const_iterator;
 
   struct HashOutputQEPrimal
@@ -195,13 +195,13 @@ class ITK_TEMPLATE_EXPORT LaplacianDeformationQuadEdgeMeshFilter:
     }
   };
 
-  using CoefficientMapType = itksys::hash_map< OutputQEPrimal*, OutputCoordRepType, HashOutputQEPrimal >;
+  using CoefficientMapType = std::unordered_map< OutputQEPrimal*, OutputCoordRepType, HashOutputQEPrimal >;
   using CoefficientMapConstIterator = typename CoefficientMapType::const_iterator;
 
-  using AreaMapType = itksys::hash_map< OutputPointIdentifier, OutputCoordRepType >;
+  using AreaMapType = std::unordered_map< OutputPointIdentifier, OutputCoordRepType >;
   using AreaMapConstIterator = typename AreaMapType::const_iterator;
 
-  using RowType = itksys::hash_map< OutputPointIdentifier, OutputCoordRepType >;
+  using RowType = std::unordered_map< OutputPointIdentifier, OutputCoordRepType >;
   using RowIterator = typename RowType::iterator;
   using RowConstIterator = typename RowType::const_iterator;
 
diff --git a/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints.h b/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints.h
index 15804debc09..a1b18059b68 100644
--- a/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints.h
+++ b/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints.h
@@ -110,7 +110,7 @@ class ITK_TEMPLATE_EXPORT LaplacianDeformationQuadEdgeMeshFilterWithSoftConstrai
   OutputCoordRepType m_Lambda;
   OutputCoordRepType m_LambdaSquare;
 
-  itksys::hash_map< OutputPointIdentifier, OutputCoordRepType > m_LocalLambdaSquare;
+  std::unordered_map< OutputPointIdentifier, OutputCoordRepType > m_LocalLambdaSquare;
 
 };
 } // end namespace itk
diff --git a/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints.hxx b/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints.hxx
index f4b80cc04cf..8c54b8ba5a3 100644
--- a/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints.hxx
+++ b/Modules/Filtering/QuadEdgeMeshFiltering/include/itkLaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints.hxx
@@ -154,7 +154,7 @@ LaplacianDeformationQuadEdgeMeshFilterWithSoftConstraints< TInputMesh, TOutputMe
 
       OutputCoordRepType l2 = m_LambdaSquare;
 
-      typename itksys::hash_map< OutputPointIdentifier, OutputCoordRepType >::const_iterator lambdaIt = this->m_LocalLambdaSquare.find( vId );
+      typename std::unordered_map< OutputPointIdentifier, OutputCoordRepType >::const_iterator lambdaIt = this->m_LocalLambdaSquare.find( vId );
       if( lambdaIt != this->m_LocalLambdaSquare.end() )
         {
         l2 = lambdaIt->second;
diff --git a/Modules/Nonunit/Review/include/itkLabelGeometryImageFilter.h b/Modules/Nonunit/Review/include/itkLabelGeometryImageFilter.h
index 554723cc38d..58659a98136 100644
--- a/Modules/Nonunit/Review/include/itkLabelGeometryImageFilter.h
+++ b/Modules/Nonunit/Review/include/itkLabelGeometryImageFilter.h
@@ -22,7 +22,7 @@
 #include "itkNumericTraits.h"
 #include "itkArray.h"
 #include "itkSimpleDataObjectDecorator.h"
-#include "itksys/hash_map.hxx"
+#include <map>
 #include <vector>
 #include "vnl/algo/vnl_symmetric_eigensystem.h"
 #include "vnl/vnl_det.h"
@@ -245,9 +245,9 @@ class ITK_TEMPLATE_EXPORT LabelGeometryImageFilter:
 
   /** Type of the map used to store data per label */
   // Map from the label to the class storing all of the geometry information.
-  using MapType = itksys::hash_map< LabelPixelType, LabelGeometry >;
-  using MapIterator = typename itksys::hash_map< LabelPixelType, LabelGeometry >::iterator;
-  using MapConstIterator = typename itksys::hash_map< LabelPixelType, LabelGeometry >::const_iterator;
+  using MapType = std::map< LabelPixelType, LabelGeometry >;
+  using MapIterator = typename std::map< LabelPixelType, LabelGeometry >::iterator;
+  using MapConstIterator = typename std::map< LabelPixelType, LabelGeometry >::const_iterator;
 
   // Macros for enabling the calculation of additional features.
   itkGetMacro(CalculatePixelIndices, bool);
diff --git a/Modules/Numerics/Statistics/include/itkKdTreeBasedKmeansEstimator.h b/Modules/Numerics/Statistics/include/itkKdTreeBasedKmeansEstimator.h
index d029a61ac96..d2f2514ea6f 100644
--- a/Modules/Numerics/Statistics/include/itkKdTreeBasedKmeansEstimator.h
+++ b/Modules/Numerics/Statistics/include/itkKdTreeBasedKmeansEstimator.h
@@ -19,7 +19,7 @@
 #define itkKdTreeBasedKmeansEstimator_h
 
 #include <vector>
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 
 #include "itkObject.h"
 #include "itkEuclideanDistanceMetric.h"
@@ -152,7 +152,7 @@ class ITK_TEMPLATE_EXPORT KdTreeBasedKmeansEstimator:
    * of changes in centroid positions)  */
   void StartOptimization();
 
-  using ClusterLabelsType = itksys::hash_map< InstanceIdentifier, unsigned int >;
+  using ClusterLabelsType = std::unordered_map< InstanceIdentifier, unsigned int >;
 
   itkSetMacro(UseClusterLabels, bool);
   itkGetConstMacro(UseClusterLabels, bool);
diff --git a/Modules/Numerics/Statistics/include/itkKdTreeBasedKmeansEstimator.hxx b/Modules/Numerics/Statistics/include/itkKdTreeBasedKmeansEstimator.hxx
index 6d4c6b580d1..cbd7f1260d9 100644
--- a/Modules/Numerics/Statistics/include/itkKdTreeBasedKmeansEstimator.hxx
+++ b/Modules/Numerics/Statistics/include/itkKdTreeBasedKmeansEstimator.hxx
@@ -404,7 +404,7 @@ KdTreeBasedKmeansEstimator< TKdTree >
     {
     m_GenerateClusterLabels = true;
     m_ClusterLabels.clear();
-    m_ClusterLabels.resize( m_KdTree->GetSample()->Size() );
+    m_ClusterLabels.rehash( m_KdTree->GetSample()->Size() );
     for ( i = 0; i < (unsigned int)( m_Parameters.size() / m_MeasurementVectorSize ); i++ )
       {
       validIndexes.push_back(i);
diff --git a/Modules/Numerics/Statistics/include/itkMembershipSample.h b/Modules/Numerics/Statistics/include/itkMembershipSample.h
index dc5e84fc48d..c50b3d4d406 100644
--- a/Modules/Numerics/Statistics/include/itkMembershipSample.h
+++ b/Modules/Numerics/Statistics/include/itkMembershipSample.h
@@ -18,7 +18,7 @@
 #ifndef itkMembershipSample_h
 #define itkMembershipSample_h
 
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 #include "itkSubsample.h"
 
 namespace itk
@@ -86,7 +86,7 @@ class ITK_TEMPLATE_EXPORT MembershipSample:public DataObject
 
   /** Typedef for the storage that holds a class label for each instance.
    * The relationship between instances and class label is one-to-one */
-  using ClassLabelHolderType = itksys::hash_map< InstanceIdentifier, ClassLabelType >;
+  using ClassLabelHolderType = std::unordered_map< InstanceIdentifier, ClassLabelType >;
 
   /** Typedef for each subsample that stores instance identifiers of instances
    * that belong to a class */
diff --git a/Modules/Segmentation/ConnectedComponents/include/itkRelabelComponentImageFilter.hxx b/Modules/Segmentation/ConnectedComponents/include/itkRelabelComponentImageFilter.hxx
index 9551e29214c..f15e90e69d0 100644
--- a/Modules/Segmentation/ConnectedComponents/include/itkRelabelComponentImageFilter.hxx
+++ b/Modules/Segmentation/ConnectedComponents/include/itkRelabelComponentImageFilter.hxx
@@ -22,7 +22,6 @@
 #include "itkImageRegionIterator.h"
 #include "itkNumericTraits.h"
 #include "itkProgressReporter.h"
-#include "itksys/hash_map.hxx"
 #include <map>
 
 namespace itk
@@ -52,7 +51,7 @@ RelabelComponentImageFilter< TInputImage, TOutputImage >
 
   // Use a map to keep track of the size of each object.  Object
   // number -> ObjectType (which has Object number and the two sizes)
-  using MapType = itksys::hash_map< LabelType, RelabelComponentObjectType >;
+  using MapType = std::map< LabelType, RelabelComponentObjectType >;
   MapType sizeMap;
   typename MapType::iterator mapIt;
   using MapValueType = typename MapType::value_type;
diff --git a/Modules/Segmentation/ConnectedComponents/test/itkRelabelComponentImageFilterTest.cxx b/Modules/Segmentation/ConnectedComponents/test/itkRelabelComponentImageFilterTest.cxx
index 022929b5d5f..b7d93607eb0 100644
--- a/Modules/Segmentation/ConnectedComponents/test/itkRelabelComponentImageFilterTest.cxx
+++ b/Modules/Segmentation/ConnectedComponents/test/itkRelabelComponentImageFilterTest.cxx
@@ -37,6 +37,7 @@ int itkRelabelComponentImageFilterTest(int argc, char* argv[] )
     return EXIT_FAILURE;
     }
 
+  bool success = true;
   using InternalPixelType = unsigned short;
   using LabelPixelType = unsigned long;
   using WritePixelType = unsigned char;
@@ -133,6 +134,7 @@ int itkRelabelComponentImageFilterTest(int argc, char* argv[] )
     {
     std::cerr << "Exception caught !" << std::endl;
     std::cerr << excep << std::endl;
+    success = false;
     }
 
 
@@ -149,6 +151,7 @@ int itkRelabelComponentImageFilterTest(int argc, char* argv[] )
     std::cerr << "Exception caught during statistics calculation!"
               << std::endl;
     std::cerr << excep << std::endl;
+    success = false;
     }
   try
     {
@@ -220,6 +223,7 @@ int itkRelabelComponentImageFilterTest(int argc, char* argv[] )
   catch (...)
     {
     std::cerr << "Exception caught while printing statistics" << std::endl;
+    success = false;
     }
 
   // Check for the sizes of the 7 first labels which should be sorted by default
@@ -230,7 +234,7 @@ int itkRelabelComponentImageFilterTest(int argc, char* argv[] )
     {
     std::cerr << "Comparing label size to reference value." << std::endl;
     std::cerr << "Got " << relabel->GetSizeOfObjectsInPixels()[i] << ", expected " << ref1[i] << std::endl;
-    return EXIT_FAILURE;
+    success = false;
     }
   }
 
@@ -239,16 +243,25 @@ int itkRelabelComponentImageFilterTest(int argc, char* argv[] )
   relabel->Update();
 
   // Check for the sizes of the 7 first labels which are no more sorted
-  unsigned long ref2 [7] = { 1491, 2, 1, 906, 3, 40, 1 };
-  for ( int i=0; i<6; ++i )
+  unsigned long ref2[7] = { 1491, 2, 1, 906, 3, 40, 1 };
+  for ( int i=0; i<7; ++i )
   {
   if ( relabel->GetSizeOfObjectsInPixels()[i] != ref2[i] )
     {
     std::cerr << "Comparing label size to reference value." << std::endl;
     std::cerr << "Got " << relabel->GetSizeOfObjectsInPixels()[i] << ", expected " << ref2[i] << std::endl;
-    return EXIT_FAILURE;
+    success = false;
     }
   }
 
-  return EXIT_SUCCESS;
+  if (success)
+    {
+    std::cout << "Test PASSED!" << std::endl;
+    return EXIT_SUCCESS;
+    }
+  else
+    {
+    std::cout << "Test FAILED!" << std::endl;
+    return EXIT_FAILURE;
+    }
 }
diff --git a/Modules/Segmentation/LevelSetsv4/include/itkLevelSetEquationTermBase.h b/Modules/Segmentation/LevelSetsv4/include/itkLevelSetEquationTermBase.h
index 00d50409874..cd6878f342d 100644
--- a/Modules/Segmentation/LevelSetsv4/include/itkLevelSetEquationTermBase.h
+++ b/Modules/Segmentation/LevelSetsv4/include/itkLevelSetEquationTermBase.h
@@ -21,7 +21,7 @@
 
 #include "itkObject.h"
 #include "itkHeavisideStepFunctionBase.h"
-#include "itksys/hash_set.hxx"
+#include <unordered_set>
 
 namespace itk
 {
@@ -129,7 +129,7 @@ class ITK_TEMPLATE_EXPORT LevelSetEquationTermBase : public Object
   /** Update the term parameter values at end of iteration */
   virtual void Update() = 0;
 
-  using RequiredDataType = itksys::hash_set< std::string >;
+  using RequiredDataType = std::unordered_set< std::string >;
 
   const RequiredDataType & GetRequiredData() const;
 
diff --git a/Modules/Segmentation/LevelSetsv4/include/itkLevelSetEquationTermContainer.h b/Modules/Segmentation/LevelSetsv4/include/itkLevelSetEquationTermContainer.h
index 02b68bec3ce..5bef9a5c7cc 100644
--- a/Modules/Segmentation/LevelSetsv4/include/itkLevelSetEquationTermContainer.h
+++ b/Modules/Segmentation/LevelSetsv4/include/itkLevelSetEquationTermContainer.h
@@ -22,7 +22,7 @@
 #include "itkLevelSetEquationTermBase.h"
 #include "itkObject.h"
 
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 
 #include <map>
 #include <string>
@@ -279,7 +279,7 @@ class ITK_TEMPLATE_EXPORT LevelSetEquationTermContainer : public Object
 
   InputImagePointer         m_Input;
 
-  using HashMapStringTermContainerType = itksys::hash_map< std::string, TermPointer >;
+  using HashMapStringTermContainerType = std::unordered_map< std::string, TermPointer >;
 
   HashMapStringTermContainerType m_NameContainer;
 
diff --git a/Modules/Segmentation/Watersheds/include/itkOneWayEquivalencyTable.h b/Modules/Segmentation/Watersheds/include/itkOneWayEquivalencyTable.h
index 9ba0ba60836..25e0e5e6b90 100644
--- a/Modules/Segmentation/Watersheds/include/itkOneWayEquivalencyTable.h
+++ b/Modules/Segmentation/Watersheds/include/itkOneWayEquivalencyTable.h
@@ -20,7 +20,7 @@
 
 
 #include "itkProcessObject.h"
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 #include "ITKWatershedsExport.h"
 
 namespace itk
@@ -57,8 +57,7 @@ class ITKWatersheds_EXPORT OneWayEquivalencyTable:public DataObject
   itkTypeMacro(OneWayEquivalencyTable, DataObject);
 
   /** Define the container type for this table */
-  using HashTableType = itksys::hash_map< unsigned long, unsigned long,
-                            itksys::hash< unsigned long > >;
+  using HashTableType = std::unordered_map< unsigned long, unsigned long >;
 
   using Iterator = HashTableType::iterator;
   using ConstIterator = HashTableType::const_iterator;
diff --git a/Modules/Segmentation/Watersheds/include/itkWatershedBoundary.h b/Modules/Segmentation/Watersheds/include/itkWatershedBoundary.h
index 57b4a7e0b7f..df6aa7ce0cd 100644
--- a/Modules/Segmentation/Watersheds/include/itkWatershedBoundary.h
+++ b/Modules/Segmentation/Watersheds/include/itkWatershedBoundary.h
@@ -23,7 +23,7 @@
 #include <vector>
 #include "itkImage.h"
 #include "itkProcessObject.h"
-#include "itksys/hash_map.hxx"
+#include <unordered_map>
 
 namespace itk
 {
@@ -115,8 +115,7 @@ class ITK_TEMPLATE_EXPORT Boundary:public DataObject
   using face_t = Image< face_pixel_t, TDimension >;
 
   /** A hash table holding flat region data structures.   */
-  using flat_hash_t = itksys::hash_map< IdentifierType, flat_region_t,
-                            itksys::hash< IdentifierType > >;
+  using flat_hash_t = std::unordered_map< IdentifierType, flat_region_t >;
   using FlatHashValueType = typename flat_hash_t::value_type;
 
   /** Itk type alias and macros defining smart pointer and type identification.
diff --git a/Modules/Segmentation/Watersheds/include/itkWatershedSegmentTable.h b/Modules/Segmentation/Watersheds/include/itkWatershedSegmentTable.h
index c60c81a5f93..f27eeaeb60f 100644
--- a/Modules/Segmentation/Watersheds/include/itkWatershedSegmentTable.h
+++ b/Modules/Segmentation/Watersheds/include/itkWatershedSegmentTable.h
@@ -90,12 +90,11 @@ class ITK_TEMPLATE_EXPORT SegmentTable:public DataObject
   };
 
   /** Define the container type for the table */
-  using HashMapType = itksys::hash_map< IdentifierType, segment_t,
-    itksys::hash< IdentifierType > >;
+  using HashMapType = std::unordered_map< IdentifierType, segment_t >;
   using Iterator = typename HashMapType::iterator;
   using ConstIterator = typename HashMapType::const_iterator;
   using ValueType = typename HashMapType::value_type;
-  using DataType = typename HashMapType::data_type;
+  using DataType = typename HashMapType::mapped_type;
 
   /** Inserts a segment into the table  */
   bool Add(IdentifierType a, const segment_t & t);
diff --git a/Modules/Segmentation/Watersheds/include/itkWatershedSegmentTreeGenerator.h b/Modules/Segmentation/Watersheds/include/itkWatershedSegmentTreeGenerator.h
index 34381d9152c..221ae48d8c1 100644
--- a/Modules/Segmentation/Watersheds/include/itkWatershedSegmentTreeGenerator.h
+++ b/Modules/Segmentation/Watersheds/include/itkWatershedSegmentTreeGenerator.h
@@ -219,8 +219,7 @@ class ITK_TEMPLATE_EXPORT SegmentTreeGenerator:public ProcessObject
   double m_FloodLevel{0.0};
   bool   m_ConsumeInput{false};
 
-  using HashMapType = itksys::hash_map< IdentifierType, bool,
-                            itksys::hash< IdentifierType > >;
+  using HashMapType = std::unordered_map< IdentifierType, bool >;
 
   OneWayEquivalencyTableType::Pointer m_MergedSegmentsTable;
 
diff --git a/Modules/Segmentation/Watersheds/include/itkWatershedSegmenter.h b/Modules/Segmentation/Watersheds/include/itkWatershedSegmenter.h
index 9a8b3fb64d1..f1c29ce66f3 100644
--- a/Modules/Segmentation/Watersheds/include/itkWatershedSegmenter.h
+++ b/Modules/Segmentation/Watersheds/include/itkWatershedSegmenter.h
@@ -244,7 +244,7 @@ class ITK_TEMPLATE_EXPORT Segmenter:
   };
 
   /** Table for storing flat region information.  */
-  using flat_region_table_t = itksys::hash_map< IdentifierType, flat_region_t, itksys::hash< IdentifierType > >;
+  using flat_region_table_t = std::unordered_map< IdentifierType, flat_region_t >;
 
   struct connectivity_t {
     unsigned int size;
@@ -256,9 +256,9 @@ class ITK_TEMPLATE_EXPORT Segmenter:
    * generating the segment table,  even though the edge tables
    * are stored as ordered lists.  An "edge" in this context
    * is synonymous with a segment "adjacency".   */
-  using edge_table_t = itksys::hash_map< IdentifierType, InputPixelType, itksys::hash< IdentifierType > >;
+  using edge_table_t = std::map< IdentifierType, InputPixelType >;
 
-  using edge_table_hash_t = itksys::hash_map< IdentifierType, edge_table_t, itksys::hash< IdentifierType > >;
+  using edge_table_hash_t = std::unordered_map< IdentifierType, edge_table_t >;
 
   Segmenter();
   Segmenter(const Self &) {}
diff --git a/Modules/Segmentation/Watersheds/test/Baseline/itkIsolatedWatershedImageFilterTest.png.md5 b/Modules/Segmentation/Watersheds/test/Baseline/itkIsolatedWatershedImageFilterTest.png.md5
index 45b63072d37..3799ff02f74 100644
--- a/Modules/Segmentation/Watersheds/test/Baseline/itkIsolatedWatershedImageFilterTest.png.md5
+++ b/Modules/Segmentation/Watersheds/test/Baseline/itkIsolatedWatershedImageFilterTest.png.md5
@@ -1 +1 @@
-b19ea6df9f910060bb62fa5e983c59f1
+ffa0ca2b5f46c024bc408c6a77b6453c
diff --git a/Modules/Segmentation/Watersheds/test/Baseline/itkIsolatedWatershedImageFilterTest.png.sha512 b/Modules/Segmentation/Watersheds/test/Baseline/itkIsolatedWatershedImageFilterTest.png.sha512
index 178c84667e9..78cbb4b4052 100644
--- a/Modules/Segmentation/Watersheds/test/Baseline/itkIsolatedWatershedImageFilterTest.png.sha512
+++ b/Modules/Segmentation/Watersheds/test/Baseline/itkIsolatedWatershedImageFilterTest.png.sha512
@@ -1 +1 @@
-15fc65785e7054a10c6ad09f3e7c5add1a6cd54d7e2e1a8171a13efbc00c699f12edca296ffb541a77fe4d294682a1f3373733d37995fd83f06660b06eb1f8ac
+dcb1e52034ab274e83b7502337ac2d22670c032a25530be41c828ade01315c014977d8ad79f4295639ff616b4df42b36cdf4007b48882410b9072a4c9a973707