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Both Great Falls National Park on the Virginia side and C&O Canal National Historic Park on the Maryland side are both national parks. You can add my C&O Canal post from a few weeks back to the collection if you’d like to. Happy to contribute!

Actually I looked it up and there are 63 National Parks in the US here is the list Maryland doesn't have any.

Looks like National Historic Parks are a different category and that’s what the C&O Canal falls into. There are 61 of them.