The 48-acre Lake Defiance, located near the center of the park, is one of the few glacial lakes in Illinois that has remained largely undeveloped, maintaining a near-natural condition.

The waters and wetlands of Moraine Hills are home to abundant wildlife; more than 200 species of birds have been identified at the park.  Fishing is available on both Lake Defiance and on the Fox River. The McHenry Dam area provides access to the Fox River, and a fishing pier accessible to visitors with disabilities is available.  More than 10 miles of trails make Moraine Hills popular for hikers, skiers and cyclists, and provide one of the park's main recreation features.

The concession stand at the McHenry Dam provides refreshments, bait and tackle, and boat rentals for both the Fox River and Lake Defiance.   ‹ ‹