Potomac is a village in Vermilion County, Illinois, United States. It is part of the 'Danville, Illinois Metropolitan Statistical Area'. The population was 681 at the 2000 census.
The town was originally named Marysville after the wives of the two founders, John Smith (a grocer) and Isaac Meneley (a blacksmith), who started businesses here in 1840. However, the Post Office found that mail was getting confused with mail for Myersville, ten miles to the east, and the name was changed to Potomac (although residents resented this and didn't accept the change for decades).
Potomac prospered into the late 20th century, with a population peaking at 900 during the 1970 census, due in part to its location along US Route 136, one of the primary East-West highways crossing the state of Illinois. The opening of Interstate 74 reduced the amount of travel through Potomac, leading to a rapid decline in the number of service stations, restaurants and small businesses in the downtown area in the early 1970s. In the early 1990s a fire destroyed several downtown buildings on the north side of Route 136, dramatically altering the appearance of the community.