Belknap is a village in Johnson County, Illinois, United States.

It was likely named for William Worth Belknap, who served as U.S. Secretary of War during this period.

[5] The village is situated in the Cache River basin northeast of Karnak and southwest of Vienna.

The Heron Pond – Little Black Slough Nature Preserve lies to the north of Belknap, and the 45-mile (72 km) Tunnel Hill State Trail passes through the village.

There were 6.1% of families and 13.2% of the population living below the poverty line, including 12.1% of under eighteens and 18.2% of those over 64.