El Dorado is a city in and the county seat of Union County, on the southern border of Arkansas, United States. According to the 2020 census, the population of the city is 17,755. El Dorado is headquarters of the Arkansas Oil and Gas Commission as well as Murphy USA, Deltic Timber Corporation and a DelekUS oil refinery. The city has a downtown arts district, the Murphy Arts District; a community college, South Arkansas College; and a multi-cultural arts center, South Arkansas Arts Center.