The state park is centered on Spring Lake, an 8.5-mile-long alluvial lake that lies parallel to the Illinois River. The lakebed lies by the foot of the river's sandstone bluff in an abandoned bed of the river. It is a shallow lake that is no more than 10 feet deep.
The lake, located in the southwestern corner of Tazewell County, has been extensively altered by dikes built in the 1900s and the 1950s. The second dike system was built around both old Spring Lake and a second, smaller lake, Saiwell Lake, and caused the two lakes to almost merge into each other. The two lakes are now only separated by a spur dike, and both lakes are now called halves of modern Spring Lake.
The nearest major town is Manito, Illinois.
There are four boat launching ramps. IDNR enforces a power limit of 25 horsepower in the lake.