During the 1920s, Colchester was the home of Henry "Kelly" Wagle, a bootlegger associated with Al Capone.

[6] U.S. Route 136 passes through the center of town as Macomb Street and North Street, leading northeast 7 miles (11 km) to Macomb, the county seat, and west 19 miles (31 km) to Carthage.

Illinois Route 110/336, a four-lane divided highway, bypasses Colchester to the south, joining US 136 3.5 miles (5.6 km) west of the city.

According to the U.S. Census Bureau, Colchester has a total area of 1.15 square miles (2.98 km2), all land.

[1] Argyle Lake State Park is 2 miles (3 km) north of Colchester.

The racial makeup of the city was 99.40% White, 0.07% Native American, 0.07% Asian, and 0.47% from two or more races.

Colchester is part of the West Prairie Community Unit School District 103.