Monroe County is a county located in the U.S. state of Arkansas. As of the 2010 census, the population was 8,149, making it the fifth-least populous county in Arkansas. The county seat is Clarendon, while its largest city is Brinkley. Monroe County is Arkansas's 20th county, formed on November 2, 1829, from portions of Arkansas and Phillips counties, and named for James Monroe, the fifth President of the United States.
Settlement in Monroe County began when Dedrick Pike settled where the Cache River enters the White River in 1816. The settlement was named Mouth of the Cache, and a post office by that name was opened years later. The community renamed itself Clarendon in 1824 in honor of the Earl of Clarendon. Monroe County was established under the Arkansas territorial legislature in 1829, and the county seat was established at Lawrenceville where a jail and courthouse were erected. A ferry across the White River came in 1836, and the county seat was moved to Clarendon in 1857, with the new brick courthouse nearly finished at the outbreak of the American Civil War. The county sent five units into Confederate service, and the Union captured Clarendon in 1863 and destroyed the city. Martial law was established for four years after the war as guerilla warfare continued and the county struggled to rebuild. The Union had completely dismandled the brick courthouse and shipped the bricks to De Valls Bluff. The Monroe County Sun was established in 1876.
It was at a site near the intersection of Monroe, Phillips, and Lee counties that surveys began shortly after the United States had completed the Louisiana Purchase. From wetlands in what would become southern Monroe County, approximately of land would be explored after President James Madison commissioned a survey of the purchase area. The point was commemorated in 1961 by the Arkansas General Assembly as part of Louisiana Purchase State Park.