Eldorado (i/ɛldəreɪdoʊ/ or /ɛldəreɪdə/) 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.
The junction of the pioneer Kaskaskia and Goshen Trails was located just south of the city. The Goshen Trail began in Old Shawneetown, Illinois and ran along the east side of Eldorado and on to the Goshen Settlement, a community near the present day East St. Louis.