The US National Park Service boasts an extensive, well-designed website that features resources for educators, nature lovers, history enthusiasts, and anyone interested in learning more about the many U.S. national parks and sites. Check out the Find a Park page, which allows you to quickly locate parks and historic sites of interest. Using the interactive map, you can find parks by state and view a variety of statistics about park visitors and land area in each state. You can also conduct a text search to find a particular park. You can also scroll down on the main page to check out a list of fee-free days at national parks.
Great mapping application!