Lake Jacksonville is a 442 acres (179 ha) reservoir located in Morgan County in the U.S. state of Illinois.

Located 4 miles (6.4 km) southeast of Jacksonville, it provides drinking water and recreational opportunities to the central Illinois city.

The reservoir drains into Big Sandy Creek, a tributary of the Illinois River.

[2][3] Lake Jacksonville is actively managed for camping, power boating, and fishing recreation.

Proof of licenses and insurance are required to lower a boat into the lake.