Eldorado (/ɛldəˈreɪdoʊ/ () or /ɛldəˈreɪdə/) is a city in Saline County, Illinois, United States. The population was 4,122 at the 2010 census, with a 1925 peak of 8,000. Although the city's name is spelled as if it were Spanish, the name was originally "Elder-Reado"—a combination of the last names of the town's two founders, Judge Samuel Elder and Joseph Read. According to legend, a signpainter for the railroad painted the name "Eldorado" on the train depot; as a result, the spelling and pronunciation was forever changed.
Eldorado is included in the Illinois–Indiana–Kentucky tri-state area and is a bedroom community in the Harrisburg micropolitan statistical area.