Phillips county lies in what is known as the Mississippi alluvia plain, also called The Delta. The earliest known inhabitants were native Indians, noted for building large earthen mounts for ceremonial purposes and to bury their chiefs.
By the time Hernando De Soto explored Arkansas in 1541 the area was home to two sophisticated Indian cultures, The Casoui and the Pacaha and included large fortified towns. The point where De Soto crossed the Mississippi River into Arkansas is much debated, with credible evidence that he crossed south of Helena into what is now Phillips County, opposite Sunflower Landing.
Between 1541 and 1803, France sold the territory known as the Louisiana Purchase, composed of 900,000 square miles to the United States for 15 million dollars.
Phillips County was created by an act of the Arkansas legislature dated May 1,1820 and named for one of its earliest settlers, Sylvanus Phillips, a member of the Territorial Legislature.