While Ohio is probably unique in having such a large grove (109 trees!), there are other Millennium Groves located across the country. Here are the ones we know about:
Millennium Grove at Norristown Farm Park; Norristown, PA - This grove shares some ancestor trees with Ohio's Millennium Grove, including Johnny Appleseed tree; Trail of Tears Redbud; Minuteman Red Maple; Mark Twain Cave Bur Oak; Franklin D. Roosevelt Redbud; Harriet Beecher Stowe White Ash.
Millennium Grove within Dunn Park; Mississauga, Ontario, Canada (not connected with the USDA's Millennium Grove project)