Jefferson County, Arkansas is a county located in the U.S. state of Arkansas in the area known as the Arkansas Delta that extends west of the Mississippi River. Jefferson County consists of five cities, two towns, and 20 townships. The county is bisected by the Arkansas River, which was critical to its development and long the chief transportation byway. In 2020, Jefferson County's population was estimated at 67,260. Its county seat and largest city is Pine Bluff. Jefferson County is included in the Pine Bluff metropolitan statistical area. The county seat and the most populous city is Pine Bluff.