Adirondack State Park
Adirondack State Park in New York is, by far, the largest state-level park in the U.S. This park covers an area of more than 6 million acres (with over 2.4 million acres directly controlled by the state). The entire Adirondack Mountain range is contained within the park, as are New York's highest mountain and more than 3,000 lakes.
This is one of the few state parks that actually has a permanent population (of more than 130,000 people), making it operationally more like a national forest than a state park. Roads make it possible to get to some of the most scenic lakes, rivers, mountains and waterfalls in the Adirondacks, though there are also hiking trails and campgrounds for people seeking a backcountry experience.