Johnson County is a county located in the U.S. state of Arkansas. As of the 2010 census, the population was 25,540. The county seat is Clarksville. Johnson County is Arkansas's 30th county, formed on November 16, 1833, from a portion of Pope County and named for Benjamin Johnson, a Territorial Judge. It is an alcohol prohibition or dry county.The Ada Mills Bridge links the Arkansas River between Johnson and Logan counties.