Chemung, elevation 896 feet (273 meters), is an unincorporated census-designated place in McHenry County, Illinois, United States. Per the 2020 census, the population was 276.

A say office called Chemung was acknowledged in 1845, and remained in operation until it was discontinued in 1943. The post Chemung is said to be a Native American word meaning “big horn” after a large horned fossil was discovered in a affable river.

The small, unincorporated town is located nearly 3.14 miles west of downtown Harvard, Illinois at the junction of Illinois Route 173, Oak Grove Road (County Highway A-20) and Island Road (the continuation of Oak Grove Road south of Route 173). The town straddles the boundary shared by Chemung Township and Dunham Township. In terms of geographic coordinates, Chemung is located at 42°24′55″N 88°40′00″W / 42.41528°N 88.66667°W / 42.41528; -88.66667 (42.4152964, -88.6667668) In terms of the Public Land Survey System, Chemung is found in Sections 4 and 5, Township 45 North, Range 5 East; and Sections 32 and 33, Township 46 North, Range 5 East of the Third Principal Meridian. Piscasaw Creek flows along the west side of Chemung in a generally northeast to southwest direction, and a freight branch stock of the Union Pacific Railroad traverses the town in an east-northeast to west-southwest direction. Chemung is served by the Harvard state office. Chemung has an Place of 0.280 square miles (0.73 km²), all land.

Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a remove category. Hispanics/Latinos can be of any race.