Out of the 63 national parks in the United States, Rocky Mountain National Park doesn't even make it into the top 10. Rocky Mountain National Park Ranks 26th by SizeAt 265,807 acres, Rocky Mountain National Park is large, but nothing in comparison to the top five largest national parks. Death Valley National Park comes in as the fifth largest national park and can fit Rocky Mountain National Park inside of its borders more than 12 times. READ MORE: Rocky Mountain National Park Reservations Return for 2026The largest national park in the United States is in Alaska. Wrangell-St. Elias National Park is massive, at 8.3 million acres, and can fit Rocky Mountain National Park within its borders over 31 times.