Eldorado () is a city in Saline County, Illinois, United States. The population was 4,122 at the 2010 census, with a 1980 peak of 5,198. Although the city’s name is spelled as if it were Spanish, the name was originally “Elderedo” or “Elder-Redo” (depending on the source)—a combination of the last names of the town’s two founders, Judge Samuel Elder, his son William, grandson Francis Marion, and neighbor Joseph Reed, and his brother William. According to legend, a signpainter for the railroad painted the name “Eldorado” on the train depot; as a result, the spelling and pronunciation (el-do-RAY-doh) 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.
Eldorado was first platted on May 24, 1858, by a surveyor named Martin D. Gillett. The post office was established on December 8 of that same year. Just before the Civil War, the first businesses were started in the town. The original village was incorporated in 1870.In the early days, Eldorado had several railroads which came through town. It was at an intersection of the Louisville & Nashville and Cairo & Vincennes railways. The “eastern extremity” of the Belleville & Eldorado Railway (St. Louis Short Line) also came through town. According to Illinois Historian Neil Gale: “This settlement, by 1896, could boast of exceptional railroad facilities – The Illinois Central, The Louisville and Nashville, and The Chicago, Cleveland, Cincinnati and St. Louis. Like several other villages, when the railroad company placed the name on the station, the name was spelled Eldorado, instead of Elderedo, and it has been known by that name since that time.”
information provided by wikipedia.org