Fairmont City is a village in St. Clair and Madison counties, Illinois, United States. The population is currently 2,635 at the 2010 census. In the 1990s Fairmont City's Hispanic population doubled, and as of 2010, over 71% of the population is of Hispanic descent. The Fairmont City Library was International Grand Prize First Place for the Libraryaware for Library-community interaction in 2017 beating out the Kansas City Public Library and Catawba County Library in North Carolina.
Fairmont City is located at 38°39′4″N 90°5′59″W (38.651200, -90.099788).
According to the 2010 census, Fairmont City has a total area of 6.591 square miles (17.07 km2), of which 6.2 square miles (16.06 km2) (or 94.07%) is land and 0.391 square miles (1.01 km2) (or 5.93%) is water.
Fairmont City is built atop portions of the Cahokia Mounds, a UNESCO World Heritage Site. The highest point in the village is Sam Chuloco Mound, an old Indian mound.
In April 2016, EPA added the Old American Zinc Fairmont City site to the National Priorities List following the Illinois EPA discovering high levels of lead, arsenic, cadmium and zinc in soil samples. Collected soil samples from properties and alleyways showed residue of arsenic, cadmium and zinc ()
Fairmont City is only about 5 minutes from the Gateway Arch of St. Louis.