diff --git a/docs/reference-guides/data/data-core.md b/docs/reference-guides/data/data-core.md
index aa493c7dcd997d..ef10d8c4c36298 100644
--- a/docs/reference-guides/data/data-core.md
+++ b/docs/reference-guides/data/data-core.md
@@ -423,7 +423,7 @@ _Parameters_
 -   _state_ `Object`: State tree.
 -   _kind_ `string`: Entity kind.
 -   _name_ `string`: Entity name.
--   _recordId_ `number`: Record ID.
+-   _recordId_ `number|string`: Record ID.
 
 _Returns_
 
diff --git a/packages/core-data/README.md b/packages/core-data/README.md
index 2dc7df4a04d71e..fd7f795b5d900a 100644
--- a/packages/core-data/README.md
+++ b/packages/core-data/README.md
@@ -670,7 +670,7 @@ _Parameters_
 -   _state_ `Object`: State tree.
 -   _kind_ `string`: Entity kind.
 -   _name_ `string`: Entity name.
--   _recordId_ `number`: Record ID.
+-   _recordId_ `number|string`: Record ID.
 
 _Returns_
 
diff --git a/packages/core-data/src/batch/default-processor.js b/packages/core-data/src/batch/default-processor.js
index 34f38ff5c3d0da..d4189550605652 100644
--- a/packages/core-data/src/batch/default-processor.js
+++ b/packages/core-data/src/batch/default-processor.js
@@ -36,6 +36,7 @@ export default async function defaultProcessor( requests ) {
 
 	const results = [];
 
+	// @ts-ignore We would have crashed or never gotten to this point if we hadn't received the maxItems count.
 	for ( const batchRequests of chunk( requests, maxItems ) ) {
 		const batchResponse = await apiFetch( {
 			path: '/batch/v1',
diff --git a/packages/core-data/src/fetch/__experimental-fetch-link-suggestions.js b/packages/core-data/src/fetch/__experimental-fetch-link-suggestions.js
index 09248d2102cda3..bb1bf41d9e2cda 100644
--- a/packages/core-data/src/fetch/__experimental-fetch-link-suggestions.js
+++ b/packages/core-data/src/fetch/__experimental-fetch-link-suggestions.js
@@ -9,7 +9,7 @@ import { __ } from '@wordpress/i18n';
 /**
  * Filters the search by type
  *
- * @typedef { 'post' | 'term' | 'post-format' } WPLinkSearchType
+ * @typedef { 'attachment' | 'post' | 'term' | 'post-format' } WPLinkSearchType
  */
 
 /**
@@ -38,6 +38,17 @@ import { __ } from '@wordpress/i18n';
  * @property {WPKind} [kind] Link kind of post-type or taxonomy
  */
 
+/**
+ * @typedef WPLinkSearchResultAugments
+ *
+ * @property {{kind: WPKind}} [meta]    Contains kind information.
+ * @property {WPKind}         [subtype] Optional subtype if it exists.
+ */
+
+/**
+ * @typedef {WPLinkSearchResult & WPLinkSearchResultAugments} WPLinkSearchResultAugmented
+ */
+
 /**
  * @typedef WPEditorSettings
  *
@@ -82,6 +93,7 @@ const fetchLinkSuggestions = async (
 
 	const { disablePostFormats = false } = settings;
 
+	/** @type {Promise<WPLinkSearchResult>[]} */
 	const queries = [];
 
 	if ( ! type || type === 'post' ) {
@@ -177,7 +189,8 @@ const fetchLinkSuggestions = async (
 	return Promise.all( queries ).then( ( results ) => {
 		return results
 			.reduce(
-				( accumulator, current ) => accumulator.concat( current ), // Flatten list.
+				( /** @type {WPLinkSearchResult[]} */ accumulator, current ) =>
+					accumulator.concat( current ), // Flatten list.
 				[]
 			)
 			.filter(
@@ -189,27 +202,24 @@ const fetchLinkSuggestions = async (
 				}
 			)
 			.slice( 0, perPage )
-			.map(
-				/**
-				 * @param {{ id: number, meta?: object, url:string, title?:string, subtype?: string, type?: string }} result
-				 */
-				( result ) => {
-					const isMedia = result.type === 'attachment';
-
-					return {
-						id: result.id,
-						url: isMedia ? result.source_url : result.url,
-						title:
-							decodeEntities(
-								isMedia
-									? result.title.rendered
-									: result.title || ''
-							) || __( '(no title)' ),
-						type: result.subtype || result.type,
-						kind: result?.meta?.kind,
-					};
-				}
-			);
+			.map( ( /** @type {WPLinkSearchResultAugmented} */ result ) => {
+				const isMedia = result.type === 'attachment';
+
+				return {
+					id: result.id,
+					// @ts-ignore fix when we make this a TS file
+					url: isMedia ? result.source_url : result.url,
+					title:
+						decodeEntities(
+							isMedia
+								? // @ts-ignore fix when we make this a TS file
+								  result.title.rendered
+								: result.title || ''
+						) || __( '(no title)' ),
+					type: result.subtype || result.type,
+					kind: result?.meta?.kind,
+				};
+			} );
 	} );
 };
 
diff --git a/packages/core-data/src/reducer.js b/packages/core-data/src/reducer.js
index b4034087bf696d..f0f93b111234d8 100644
--- a/packages/core-data/src/reducer.js
+++ b/packages/core-data/src/reducer.js
@@ -16,6 +16,8 @@ import { ifMatchingAction, replaceAction } from './utils';
 import { reducer as queriedDataReducer } from './queried-data';
 import { rootEntitiesConfig, DEFAULT_ENTITY_KEY } from './entities';
 
+/** @typedef {import('./types').AnyFunction} AnyFunction */
+
 /**
  * Reducer managing terms state. Keyed by taxonomy slug, the value is either
  * undefined (if no request has been made for given taxonomy), null (if a
@@ -185,7 +187,7 @@ export function themeGlobalStyleVariations( state = {}, action ) {
  *
  * @param {Object} entityConfig Entity config.
  *
- * @return {Function} Reducer.
+ * @return {AnyFunction} Reducer.
  */
 function entity( entityConfig ) {
 	return flowRight( [
@@ -406,7 +408,11 @@ export const entities = ( state = {}, action ) => {
 
 /** @typedef {Array<Object> & UndoStateMeta} UndoState */
 
-/** @type {UndoState} */
+/**
+ * @type {UndoState}
+ *
+ * @todo Given how we use this we might want to make a custom class for it.
+ */
 const UNDO_INITIAL_STATE = Object.assign( [], { offset: 0 } );
 
 /** @type {Object} */
@@ -416,7 +422,7 @@ let lastEditAction;
  * Reducer keeping track of entity edit undo history.
  *
  * @param {UndoState} state  Current state.
- * @param {Object} action Dispatched action.
+ * @param {Object}    action Dispatched action.
  *
  * @return {UndoState} Updated state.
  */
@@ -455,6 +461,7 @@ export function undo( state = UNDO_INITIAL_STATE, action ) {
 			let nextState;
 
 			if ( isUndoOrRedo ) {
+				// @ts-ignore we might consider using Object.assign({}, state)
 				nextState = [ ...state ];
 				nextState.offset =
 					state.offset + ( action.meta.isUndo ? -1 : 1 );
@@ -494,6 +501,7 @@ export function undo( state = UNDO_INITIAL_STATE, action ) {
 					( key ) => ! action.transientEdits[ key ]
 				)
 			) {
+				// @ts-ignore we might consider using Object.assign({}, state)
 				nextState = [ ...state ];
 				nextState.flattenedUndo = {
 					...state.flattenedUndo,
@@ -505,6 +513,7 @@ export function undo( state = UNDO_INITIAL_STATE, action ) {
 
 			// Clear potential redos, because this only supports linear history.
 			nextState =
+				// @ts-ignore this needs additional cleanup, probably involving code-level changes
 				nextState || state.slice( 0, state.offset || undefined );
 			nextState.offset = nextState.offset || 0;
 			nextState.pop();
diff --git a/packages/core-data/src/selectors.js b/packages/core-data/src/selectors.js
index 67cd6b1aa5087e..279fd032d8581b 100644
--- a/packages/core-data/src/selectors.js
+++ b/packages/core-data/src/selectors.js
@@ -501,10 +501,10 @@ export const getEntityRecordNonTransientEdits = createSelector(
  * Returns true if the specified entity record has edits,
  * and false otherwise.
  *
- * @param {Object} state    State tree.
- * @param {string} kind     Entity kind.
- * @param {string} name     Entity name.
- * @param {number} recordId Record ID.
+ * @param {Object}        state    State tree.
+ * @param {string}        kind     Entity kind.
+ * @param {string}        name     Entity name.
+ * @param {number|string} recordId Record ID.
  *
  * @return {boolean} Whether the entity record has edits or not.
  */
diff --git a/packages/core-data/src/utils/if-matching-action.js b/packages/core-data/src/utils/if-matching-action.js
index bbbe35800187bd..022c4211a8a284 100644
--- a/packages/core-data/src/utils/if-matching-action.js
+++ b/packages/core-data/src/utils/if-matching-action.js
@@ -1,11 +1,13 @@
+/** @typedef {import('../types').AnyFunction} AnyFunction */
+
 /**
  * A higher-order reducer creator which invokes the original reducer only if
  * the dispatching action matches the given predicate, **OR** if state is
  * initializing (undefined).
  *
- * @param {Function} isMatch Function predicate for allowing reducer call.
+ * @param {AnyFunction} isMatch Function predicate for allowing reducer call.
  *
- * @return {Function} Higher-order reducer.
+ * @return {AnyFunction} Higher-order reducer.
  */
 const ifMatchingAction = ( isMatch ) => ( reducer ) => ( state, action ) => {
 	if ( state === undefined || isMatch( action ) ) {
diff --git a/packages/core-data/src/utils/replace-action.js b/packages/core-data/src/utils/replace-action.js
index 91cecb0e391513..92f22c22dd1bff 100644
--- a/packages/core-data/src/utils/replace-action.js
+++ b/packages/core-data/src/utils/replace-action.js
@@ -1,10 +1,12 @@
+/** @typedef {import('../types').AnyFunction} AnyFunction */
+
 /**
  * Higher-order reducer creator which substitutes the action object before
  * passing to the original reducer.
  *
- * @param {Function} replacer Function mapping original action to replacement.
+ * @param {AnyFunction} replacer Function mapping original action to replacement.
  *
- * @return {Function} Higher-order reducer.
+ * @return {AnyFunction} Higher-order reducer.
  */
 const replaceAction = ( replacer ) => ( reducer ) => ( state, action ) => {
 	return reducer( state, replacer( action ) );
diff --git a/packages/core-data/tsconfig.json b/packages/core-data/tsconfig.json
new file mode 100644
index 00000000000000..35d05d8fa3b033
--- /dev/null
+++ b/packages/core-data/tsconfig.json
@@ -0,0 +1,20 @@
+{
+	"extends": "../../tsconfig.base.json",
+	"compilerOptions": {
+		"rootDir": "src",
+		"declarationDir": "build-types",
+		"noUnusedParameters": false,
+		"noImplicitAny": false
+	},
+	"references": [
+		{ "path": "../compose" },
+		{ "path": "../deprecated" },
+		{ "path": "../data" },
+		{ "path": "../element" },
+		{ "path": "../is-shallow-equal" },
+		{ "path": "../priority-queue" },
+		{ "path": "../redux-routine" },
+		{ "path": "../url" }
+	],
+	"include": [ "src/**/*.js", "src/**/*.tsx", "src/**/*.ts" ]
+}
diff --git a/tsconfig.json b/tsconfig.json
index 8a78ab8e69a83a..8486f2dba941b7 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -8,6 +8,7 @@
 		{ "path": "packages/block-editor" },
 		{ "path": "packages/components" },
 		{ "path": "packages/compose" },
+		{ "path": "packages/core-data" },
 		{ "path": "packages/data" },
 		{ "path": "packages/date" },
 		{ "path": "packages/deprecated" },