diff --git a/dev/tools/localization/bin/gen_date_localizations.dart b/dev/tools/localization/bin/gen_date_localizations.dart
index 7507648407..5da786a05e 100644
--- a/dev/tools/localization/bin/gen_date_localizations.dart
+++ b/dev/tools/localization/bin/gen_date_localizations.dart
@@ -75,6 +75,7 @@ Future<void> main(List<String> rawArgs) async {
   final Directory datePatternsDirectory = Directory(path.join(pathToIntl, 'src', 'data', 'dates', 'patterns'));
   final Map<String, File> patternFiles = _listIntlData(datePatternsDirectory);
   final StringBuffer buffer = StringBuffer();
+  final Set<String> supportedLocales = _supportedLocales();
 
   buffer.writeln(
 '''
@@ -94,7 +95,7 @@ Future<void> main(List<String> rawArgs) async {
   buffer.writeln('const Map<String, dynamic> dateSymbols = <String, dynamic> {');
   symbolFiles.forEach((String locale, File data) {
     currentLocale = locale;
-    if (_supportedLocales().contains(locale))
+    if (supportedLocales.contains(locale))
       buffer.writeln(_jsonToMapEntry(locale, json.decode(data.readAsStringSync())));
   });
   currentLocale = null;
@@ -107,7 +108,7 @@ Future<void> main(List<String> rawArgs) async {
 /// supported by flutter_localizations.''');
   buffer.writeln('const Map<String, Map<String, String>> datePatterns = <String, Map<String, String>> {');
   patternFiles.forEach((String locale, File data) {
-    if (_supportedLocales().contains(locale)) {
+    if (supportedLocales.contains(locale)) {
       final Map<String, dynamic> patterns = json.decode(data.readAsStringSync()) as Map<String, dynamic>;
       buffer.writeln("'$locale': <String, String>{");
       patterns.forEach((String key, dynamic value) {
@@ -164,13 +165,21 @@ String _jsonToMap(dynamic json) {
 }
 
 Set<String> _supportedLocales() {
-  final Set<String> supportedLocales = <String>{};
+  // Assumes that en_US is a supported locale by default. Without this, usage
+  // of the intl package APIs before Flutter populates its set of supported i18n
+  // date patterns and symbols may cause problems.
+  //
+  // For more context, see https://github.com/flutter/flutter/issues/67644.
+  final Set<String> supportedLocales = <String>{
+    'en_US',
+  };
   final RegExp filenameRE = RegExp(r'(?:material|cupertino)_(\w+)\.arb$');
   final Directory supportedLocalesDirectory = Directory(path.join('packages', 'flutter_localizations', 'lib', 'src', 'l10n'));
   for (final FileSystemEntity entity in supportedLocalesDirectory.listSync()) {
     final String filePath = entity.path;
-    if (FileSystemEntity.isFileSync(filePath) && filenameRE.hasMatch(filePath))
+    if (FileSystemEntity.isFileSync(filePath) && filenameRE.hasMatch(filePath)) {
       supportedLocales.add(filenameRE.firstMatch(filePath)[1]);
+    }
   }
 
   return supportedLocales;
diff --git a/packages/flutter_localizations/lib/src/l10n/generated_date_localizations.dart b/packages/flutter_localizations/lib/src/l10n/generated_date_localizations.dart
index dde7b2ac3c..04f1869599 100644
--- a/packages/flutter_localizations/lib/src/l10n/generated_date_localizations.dart
+++ b/packages/flutter_localizations/lib/src/l10n/generated_date_localizations.dart
@@ -4001,6 +4001,196 @@ const Map<String, dynamic> dateSymbols = <String, dynamic>{
       '{1}, {0}',
     ],
   },
+  'en_US': <String, dynamic>{
+    'NAME': 'en_US',
+    'ERAS': <dynamic>[
+      'BC',
+      'AD',
+    ],
+    'ERANAMES': <dynamic>[
+      'Before Christ',
+      'Anno Domini',
+    ],
+    'NARROWMONTHS': <dynamic>[
+      'J',
+      'F',
+      'M',
+      'A',
+      'M',
+      'J',
+      'J',
+      'A',
+      'S',
+      'O',
+      'N',
+      'D',
+    ],
+    'STANDALONENARROWMONTHS': <dynamic>[
+      'J',
+      'F',
+      'M',
+      'A',
+      'M',
+      'J',
+      'J',
+      'A',
+      'S',
+      'O',
+      'N',
+      'D',
+    ],
+    'MONTHS': <dynamic>[
+      'January',
+      'February',
+      'March',
+      'April',
+      'May',
+      'June',
+      'July',
+      'August',
+      'September',
+      'October',
+      'November',
+      'December',
+    ],
+    'STANDALONEMONTHS': <dynamic>[
+      'January',
+      'February',
+      'March',
+      'April',
+      'May',
+      'June',
+      'July',
+      'August',
+      'September',
+      'October',
+      'November',
+      'December',
+    ],
+    'SHORTMONTHS': <dynamic>[
+      'Jan',
+      'Feb',
+      'Mar',
+      'Apr',
+      'May',
+      'Jun',
+      'Jul',
+      'Aug',
+      'Sep',
+      'Oct',
+      'Nov',
+      'Dec',
+    ],
+    'STANDALONESHORTMONTHS': <dynamic>[
+      'Jan',
+      'Feb',
+      'Mar',
+      'Apr',
+      'May',
+      'Jun',
+      'Jul',
+      'Aug',
+      'Sep',
+      'Oct',
+      'Nov',
+      'Dec',
+    ],
+    'WEEKDAYS': <dynamic>[
+      'Sunday',
+      'Monday',
+      'Tuesday',
+      'Wednesday',
+      'Thursday',
+      'Friday',
+      'Saturday',
+    ],
+    'STANDALONEWEEKDAYS': <dynamic>[
+      'Sunday',
+      'Monday',
+      'Tuesday',
+      'Wednesday',
+      'Thursday',
+      'Friday',
+      'Saturday',
+    ],
+    'SHORTWEEKDAYS': <dynamic>[
+      'Sun',
+      'Mon',
+      'Tue',
+      'Wed',
+      'Thu',
+      'Fri',
+      'Sat',
+    ],
+    'STANDALONESHORTWEEKDAYS': <dynamic>[
+      'Sun',
+      'Mon',
+      'Tue',
+      'Wed',
+      'Thu',
+      'Fri',
+      'Sat',
+    ],
+    'NARROWWEEKDAYS': <dynamic>[
+      'S',
+      'M',
+      'T',
+      'W',
+      'T',
+      'F',
+      'S',
+    ],
+    'STANDALONENARROWWEEKDAYS': <dynamic>[
+      'S',
+      'M',
+      'T',
+      'W',
+      'T',
+      'F',
+      'S',
+    ],
+    'SHORTQUARTERS': <dynamic>[
+      'Q1',
+      'Q2',
+      'Q3',
+      'Q4',
+    ],
+    'QUARTERS': <dynamic>[
+      '1st quarter',
+      '2nd quarter',
+      '3rd quarter',
+      '4th quarter',
+    ],
+    'AMPMS': <dynamic>[
+      'AM',
+      'PM',
+    ],
+    'DATEFORMATS': <dynamic>[
+      'EEEE, MMMM d, y',
+      'MMMM d, y',
+      'MMM d, y',
+      'M/d/yy',
+    ],
+    'TIMEFORMATS': <dynamic>[
+      'h:mm:ss a zzzz',
+      'h:mm:ss a z',
+      'h:mm:ss a',
+      'h:mm a',
+    ],
+    'AVAILABLEFORMATS': null,
+    'FIRSTDAYOFWEEK': 6,
+    'WEEKENDRANGE': <dynamic>[
+      5,
+      6,
+    ],
+    'FIRSTWEEKCUTOFFDAY': 5,
+    'DATETIMEFORMATS': <dynamic>[
+      '{1} \'at\' {0}',
+      '{1} \'at\' {0}',
+      '{1}, {0}',
+      '{1}, {0}',
+    ],
+  },
   'en_ZA': <String, dynamic>{
     'NAME': 'en_ZA',
     'ERAS': <dynamic>[
@@ -18658,6 +18848,52 @@ const Map<String, Map<String, String>> datePatterns =
     'zzzz': 'zzzz',
     'ZZZZ': 'ZZZZ',
   },
+  'en_US': <String, String>{
+    'd': 'd',
+    'E': 'ccc',
+    'EEEE': 'cccc',
+    'LLL': 'LLL',
+    'LLLL': 'LLLL',
+    'M': 'L',
+    'Md': 'M/d',
+    'MEd': 'EEE, M/d',
+    'MMM': 'LLL',
+    'MMMd': 'MMM d',
+    'MMMEd': 'EEE, MMM d',
+    'MMMM': 'LLLL',
+    'MMMMd': 'MMMM d',
+    'MMMMEEEEd': 'EEEE, MMMM d',
+    'QQQ': 'QQQ',
+    'QQQQ': 'QQQQ',
+    'y': 'y',
+    'yM': 'M/y',
+    'yMd': 'M/d/y',
+    'yMEd': 'EEE, M/d/y',
+    'yMMM': 'MMM y',
+    'yMMMd': 'MMM d, y',
+    'yMMMEd': 'EEE, MMM d, y',
+    'yMMMM': 'MMMM y',
+    'yMMMMd': 'MMMM d, y',
+    'yMMMMEEEEd': 'EEEE, MMMM d, y',
+    'yQQQ': 'QQQ y',
+    'yQQQQ': 'QQQQ y',
+    'H': 'HH',
+    'Hm': 'HH:mm',
+    'Hms': 'HH:mm:ss',
+    'j': 'h a',
+    'jm': 'h:mm a',
+    'jms': 'h:mm:ss a',
+    'jmv': 'h:mm a v',
+    'jmz': 'h:mm a z',
+    'jz': 'h a z',
+    'm': 'm',
+    'ms': 'mm:ss',
+    's': 's',
+    'v': 'v',
+    'z': 'z',
+    'zzzz': 'zzzz',
+    'ZZZZ': 'ZZZZ',
+  },
   'en_ZA': <String, String>{
     'd': 'd',
     'E': 'ccc',
diff --git a/packages/flutter_localizations/lib/src/utils/date_localizations.dart b/packages/flutter_localizations/lib/src/utils/date_localizations.dart
index 9b0abd856b..b6768090a6 100644
--- a/packages/flutter_localizations/lib/src/utils/date_localizations.dart
+++ b/packages/flutter_localizations/lib/src/utils/date_localizations.dart
@@ -9,17 +9,18 @@ import '../l10n/generated_date_localizations.dart' as date_localizations;
 /// Tracks if date i18n data has been loaded.
 bool _dateIntlDataInitialized = false;
 
-/// Loads i18n data for dates if it hasn't be loaded yet.
+/// Loads i18n data for dates if it hasn't been loaded yet.
 ///
-/// Only the first invocation of this function has the effect of loading the
-/// data. Subsequent invocations have no effect.
+/// Only the first invocation of this function loads the data. Subsequent
+/// invocations have no effect.
 void loadDateIntlDataIfNotLoaded() {
   if (!_dateIntlDataInitialized) {
     // TODO(garyq): Add support for scriptCodes. Do not strip scriptCode from string.
 
-    // Keep track of initialzed locales, or will fail on attempted double init.
-    // This can only happen if a locale with a stripped scriptCode has already
-    // been initialzed. This should be removed when scriptCode stripping is removed.
+    // Keeps track of initialized locales. This can only happen if a locale
+    // with a stripped scriptCode has already been initialzed. The set of
+    // initialized locales should be removed when scriptCode stripping is
+    // removed.
     final Set<String> initializedLocales = <String>{};
     date_localizations.dateSymbols
       .cast<String, Map<String, dynamic>>()
diff --git a/packages/flutter_localizations/test/material/date_time_test.dart b/packages/flutter_localizations/test/material/date_time_test.dart
index 0b7960630a..1b475f27d8 100644
--- a/packages/flutter_localizations/test/material/date_time_test.dart
+++ b/packages/flutter_localizations/test/material/date_time_test.dart
@@ -7,6 +7,7 @@ import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:intl/intl.dart';
 
 void main() {
   group(GlobalMaterialLocalizations, () {
@@ -159,6 +160,28 @@ void main() {
       });
     });
   });
+
+  // Regression test for https://github.com/flutter/flutter/issues/67644.
+  testWidgets('en_US is initialized correctly by Flutter when DateFormat is used', (WidgetTester tester) async {
+    DateFormat dateFormat;
+
+    await tester.pumpWidget(MaterialApp(
+      supportedLocales: const <Locale>[
+        Locale('en', 'US'),
+      ],
+      locale: const Locale('en', 'US'),
+      localizationsDelegates: const <LocalizationsDelegate<dynamic>>[
+        GlobalMaterialLocalizations.delegate,
+      ],
+      home: Builder(builder: (BuildContext context) {
+        dateFormat = DateFormat('EEE, d MMM yyyy HH:mm:ss', 'en_US');
+
+        return Container();
+      }),
+    ));
+
+    expect(dateFormat?.locale, 'en_US');
+  });
 }
 
 enum DateType { year, medium, full, monthYear }