Arkadelphia is a city in Clark County, Arkansas, United States. As of the 2010 census, the population was 10,714. The city is the county seat of Clark County. It is situated at the foothills of the Ouachita Mountains. Two universities, Henderson State University and Ouachita Baptist University, are located there. Arkadelphia was incorporated in 1857.HistoryThe site was settled in about 1809 by John Hemphill, operator of a nearby salt works, Arkansas's first industry. It was known as Blakelytown until 1839, when the settlement adopted the name Arkadelphia. Origin of the name "Arkadelphia" is uncertain. One possibility is that it was formed by combining Ark- from the state's name Arkansas and adelphia from the Greek meaning "brother/place".Another explanation of the name is a combination of "adelphia" for place and "arc." Arkadelphia was once known as the "City of Rainbows," perhaps because the humid climate often resulted in rain.GeographyArkadelphia is located in northeastern Clark County at, on the west bank of the Ouachita River. According to the United States Census Bureau, the city has a total area of 18.9sqkm, of which 18.8sqkm is land and 0.1sqkm, or 0.49%, is water.