diff --git a/packages/eslint-plugin/src/rules/prefer-readonly-parameter-types.ts b/packages/eslint-plugin/src/rules/prefer-readonly-parameter-types.ts
index fdf48395eae5..da13a0657e78 100644
--- a/packages/eslint-plugin/src/rules/prefer-readonly-parameter-types.ts
+++ b/packages/eslint-plugin/src/rules/prefer-readonly-parameter-types.ts
@@ -1,6 +1,7 @@
 import {
   TSESTree,
   AST_NODE_TYPES,
+  ESLintUtils,
 } from '@typescript-eslint/experimental-utils';
 import * as util from '../util';
 
@@ -8,7 +9,7 @@ type Options = [
   {
     checkParameterProperties?: boolean;
     ignoreInferredTypes?: boolean;
-  } & util.ReadonlynessOptions,
+  } & ESLintUtils.ReadonlynessOptions,
 ];
 type MessageIds = 'shouldBeReadonly';
 
@@ -34,7 +35,7 @@ export default util.createRule<Options, MessageIds>({
           ignoreInferredTypes: {
             type: 'boolean',
           },
-          ...util.readonlynessOptionsSchema.properties,
+          ...ESLintUtils.readonlynessOptionsSchema.properties,
         },
       },
     ],
@@ -46,7 +47,7 @@ export default util.createRule<Options, MessageIds>({
     {
       checkParameterProperties: true,
       ignoreInferredTypes: false,
-      ...util.readonlynessOptionsDefaults,
+      ...ESLintUtils.readonlynessOptionsDefaults,
     },
   ],
   create(context, options) {
@@ -98,7 +99,7 @@ export default util.createRule<Options, MessageIds>({
 
           const tsNode = esTreeNodeToTSNodeMap.get(actualParam);
           const type = checker.getTypeAtLocation(tsNode);
-          const isReadOnly = util.isTypeReadonly(checker, type, {
+          const isReadOnly = ESLintUtils.isTypeReadonly(checker, type, {
             treatMethodsAsReadonly: treatMethodsAsReadonly!,
           });
 
diff --git a/packages/eslint-plugin/src/util/explicitReturnTypeUtils.ts b/packages/eslint-plugin/src/util/explicitReturnTypeUtils.ts
index c05d6c6dab35..a4d4f92f6ddd 100644
--- a/packages/eslint-plugin/src/util/explicitReturnTypeUtils.ts
+++ b/packages/eslint-plugin/src/util/explicitReturnTypeUtils.ts
@@ -3,9 +3,14 @@ import {
   AST_NODE_TYPES,
   TSESLint,
 } from '@typescript-eslint/experimental-utils';
-import { isTypeAssertion, isConstructor, isSetter } from './astUtils';
-import { getFunctionHeadLoc } from './getFunctionHeadLoc';
-import { nullThrows, NullThrowsReasons } from './nullThrows';
+import {
+  isTypeAssertion,
+  isConstructor,
+  isSetter,
+  getFunctionHeadLoc,
+  nullThrows,
+  NullThrowsReasons,
+} from '.';
 
 type FunctionExpression =
   | TSESTree.ArrowFunctionExpression
diff --git a/packages/eslint-plugin/src/util/index.ts b/packages/eslint-plugin/src/util/index.ts
index 4c0284895235..fafd43cded0a 100644
--- a/packages/eslint-plugin/src/util/index.ts
+++ b/packages/eslint-plugin/src/util/index.ts
@@ -6,17 +6,21 @@ export * from './createRule';
 export * from './getFunctionHeadLoc';
 export * from './getThisExpression';
 export * from './getWrappingFixer';
-export * from './isTypeReadonly';
 export * from './misc';
-export * from './nullThrows';
 export * from './objectIterators';
-export * from './propertyTypes';
 export * from './requiresQuoting';
 export * from './types';
 
 // this is done for convenience - saves migrating all of the old rules
-const { applyDefault, deepMerge, isObjectNotArray, getParserServices } =
-  ESLintUtils;
+const {
+  applyDefault,
+  deepMerge,
+  isObjectNotArray,
+  getParserServices,
+  getTypeOfPropertyOfName,
+  nullThrows,
+  NullThrowsReasons,
+} = ESLintUtils;
 type InferMessageIdsTypeFromRule<T> =
   ESLintUtils.InferMessageIdsTypeFromRule<T>;
 type InferOptionsTypeFromRule<T> = ESLintUtils.InferOptionsTypeFromRule<T>;
@@ -26,6 +30,9 @@ export {
   deepMerge,
   isObjectNotArray,
   getParserServices,
+  getTypeOfPropertyOfName,
+  nullThrows,
+  NullThrowsReasons,
   InferMessageIdsTypeFromRule,
   InferOptionsTypeFromRule,
 };
diff --git a/packages/experimental-utils/package.json b/packages/experimental-utils/package.json
index 779d7f1e61b6..4f73792b24f6 100644
--- a/packages/experimental-utils/package.json
+++ b/packages/experimental-utils/package.json
@@ -44,7 +44,8 @@
     "@typescript-eslint/types": "4.30.0",
     "@typescript-eslint/typescript-estree": "4.30.0",
     "eslint-scope": "^5.1.1",
-    "eslint-utils": "^3.0.0"
+    "eslint-utils": "^3.0.0",
+    "tsutils": "^3.21.0"
   },
   "peerDependencies": {
     "eslint": "*"
diff --git a/packages/experimental-utils/src/eslint-utils/index.ts b/packages/experimental-utils/src/eslint-utils/index.ts
index bbbe8df2709f..d1448ed508d2 100644
--- a/packages/experimental-utils/src/eslint-utils/index.ts
+++ b/packages/experimental-utils/src/eslint-utils/index.ts
@@ -5,3 +5,6 @@ export * from './InferTypesFromRule';
 export * from './RuleCreator';
 export * from './RuleTester';
 export * from './deepMerge';
+export * from './isTypeReadonly';
+export * from './propertyTypes';
+export * from './nullThrows';
diff --git a/packages/eslint-plugin/src/util/isTypeReadonly.ts b/packages/experimental-utils/src/eslint-utils/isTypeReadonly.ts
similarity index 100%
rename from packages/eslint-plugin/src/util/isTypeReadonly.ts
rename to packages/experimental-utils/src/eslint-utils/isTypeReadonly.ts
diff --git a/packages/eslint-plugin/src/util/nullThrows.ts b/packages/experimental-utils/src/eslint-utils/nullThrows.ts
similarity index 100%
rename from packages/eslint-plugin/src/util/nullThrows.ts
rename to packages/experimental-utils/src/eslint-utils/nullThrows.ts
diff --git a/packages/eslint-plugin/src/util/propertyTypes.ts b/packages/experimental-utils/src/eslint-utils/propertyTypes.ts
similarity index 100%
rename from packages/eslint-plugin/src/util/propertyTypes.ts
rename to packages/experimental-utils/src/eslint-utils/propertyTypes.ts
diff --git a/packages/experimental-utils/typings/typescript.d.ts b/packages/experimental-utils/typings/typescript.d.ts
new file mode 100644
index 000000000000..73304155ee74
--- /dev/null
+++ b/packages/experimental-utils/typings/typescript.d.ts
@@ -0,0 +1,33 @@
+import 'typescript';
+
+declare module 'typescript' {
+  interface TypeChecker {
+    // internal TS APIs
+
+    /**
+     * @returns `true` if the given type is an array type:
+     * - `Array<foo>`
+     * - `ReadonlyArray<foo>`
+     * - `foo[]`
+     * - `readonly foo[]`
+     */
+    isArrayType(type: Type): type is TypeReference;
+    /**
+     * @returns `true` if the given type is a tuple type:
+     * - `[foo]`
+     * - `readonly [foo]`
+     */
+    isTupleType(type: Type): type is TupleTypeReference;
+    /**
+     * Return the type of the given property in the given type, or undefined if no such property exists
+     */
+    getTypeOfPropertyOfType(type: Type, propertyName: string): Type | undefined;
+  }
+
+  interface Type {
+    /**
+     * If the type is `any`, and this is set to "error", then TS was unable to resolve the type
+     */
+    intrinsicName?: string;
+  }
+}