El Dorado is a city in and the county seat of Union County, Arkansas, USA. According to estimates, the 2012 census, the population of the city is 18,491.El Dorado is headquarters of the Arkansas Oil and Gas Commission as well as Murphy Oil, Murphy USA, Deltic Timber Corporation, and the Lion Oil Refinery. The city contains a community college, South Arkansas Community College, a multi-cultural arts center: South Arkansas Arts Center. El Dorado is the population, cultural, and business center of the regional area. The city is best known as being the heart of the 1920s oil boom in southern Arkansas. Its nickname is "Arkansas’s Original Boomtown". El Dorado is located about 100 miles from the state capital of Little Rock.