The county was founded on December 31, 1833, after most of the Choctaw Nation was forced out under Indian Removal.

In 1833 the federal government opened the land for settlement by European Americans after the Choctaw were relocated to Indian Territory west of the Mississippi River, in what is now Oklahoma.

Colonel Thomas Bailey came from Kentucky and formed the first European-American settlement on the north fork of the creek, which was about five miles to the northeast.

He was later joined by James Bailey, Samuel Caruthers, William Flemming, M. Johnson, Willam Kendrick, Robert Thrasher, A. Patterson, and Kinchen Mayo, who extended the settlement along the creek toward the Junction.

DeKalb and Tillatoba were founded on the north fork of the creek just west of the present town.

Both towns wanted to be county seat of Tallahatchie, and Tillatoba gained the distinction.

Under the Dancing Rabbit Treaty of 1830, this section of land had been granted to Greenwood LeFlore, the leading Choctaw chief.

From 1882 through 1884 disastrous floods and overflows of the Tallahatchie River forced the people of Sumner to go by boat for supplies to Webb (which was at the time called Hood).

Sumner's county courthouse was the site of the 1955 murder trial of two white men, J.W.

Milam and Roy Bryant, accused in the lynching and murder of Emmett Till that year in adjoining Leflore County.

They were acquitted by an all-white jury of the murder of Till, a teenage African-American boy from Chicago.

In 1990, the courthouse was designated as a state landmark by the Mississippi Department of Archives and History.

That same year, in nearby Glendora, Mississippi, resident Elmer Kimbrell shot and killed African-American Clinton Melton in front of three witnesses after an argument about how much gas Melton pumped into Kimbrell's car.

[5] As of the 2020 United States Census, there were 12,715 people, 4,369 households, and 2,775 families residing in the county.