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.