Emmett Till was the son of Mamie Carthan (1921–2003) and Louis Till (1922–1945). Emmett's mother was born in the small Delta town of Webb, Mississippi. The Delta region encompasses the large, multi-county area of northwestern Mississippi in the watershed of the Yazoo and Mississippi rivers. When Carthan was two years old, her family moved to Argo, Illinois, as part of the Great Migration of black families to the North to escape lack of opportunity and unequal treatment under the law. Argo received so many Southern migrants it was named "Little Mississippi"; Carthan's mother's home was often used as a way station for people who had just moved from the South as they were trying to find jobs and homes. Mississippi was the poorest state in the U.S. in the 1950s, and the Delta counties were some of the poorest in Mississippi. In Tallahatchie County, where Mamie Carthan was born, the average income per household in 1949 was $690 ($6,755 in 2013 dollars); for black families it was $462 ($4,523 in 2013 dollars). Economic opportunities for blacks were almost nonexistent. Most of them were sharecroppers who lived on land owned by whites. Blacks had essentially not been allowed to vote since the white-dominated legislature passed a new constitution in 1890, were excluded from politics, and had very few legal rights.
Till was born in Chicago and nicknamed "Bobo" as an infant by a family friend. His mother Mamie largely raised him with her mother; she and Louis Till separated in 1942 after she discovered he had been unfaithful. Louis later choked her to unconsciousness, to which she responded by throwing scalding water at him. For violating court orders to stay away from Mamie, Emmett's father Louis was forced by a judge to choose between jail or enlisting in the U.S. Army in 1943; he was executed in Italy in 1945 after being convicted of rape and murder by a court-martial. At the age of six Emmett contracted polio, leaving him with a persistent stutter. Mamie and Emmett moved to Detroit, where she met and married "Pink" Bradley in 1951. Emmett preferred to live in Chicago, so he relocated to live with his grandmother; his mother and stepfather rejoined him later that year. After the marriage dissolved in 1952, Bradley returned to Detroit.
Mamie Till Bradley and Emmett lived alone together in a busy neighborhood in Chicago's South Side, near extended relatives. She began working as a civilian clerk for the U.S. Air Force for a better salary and recalled that Emmett was industrious enough to help with chores at home, although he sometimes got distracted. His mother remembered that he did not know his own limitations at times. Following his and Mamie's separation, Bradley visited and began threatening her. At eleven years old, Emmett, with a butcher knife in hand, told Bradley he would kill him if Bradley did not leave. Usually, however, Emmett was happy. He and his cousins and friends pulled pranks on each other (Emmett once took advantage of an extended car ride when his friend fell asleep and placed the friend's underwear on his head), and spent their free time in pickup baseball games. He was a natty dresser and often the center of attention among his peers.
In 1955, Emmett was stocky and muscular, weighing about 150 pounds (68 kg) and standing 5 feet 4 inches (1.63 m). Despite his being only 14 years old, whites in Mississippi claimed Till looked like an adult. Mamie Till Bradley's uncle, 64-year-old Mose Wright, visited her and Emmett in Chicago during the summer and told Emmett stories about living in the Mississippi Delta. Emmett wanted to see for himself. Bradley was ready for a vacation and planned to take Emmett with her, but after he begged her to visit Wright, she relented. Wright planned to accompany Till with a cousin, Wheeler Parker, and another, Curtis Jones, would join them soon. Wright was a sharecropper and part-time minister who was often called "Preacher". He lived in Money, Mississippi, a small town in the Delta that consisted of three stores, a school, a post office, a cotton gin, and a couple hundred residents, 8 miles (13 km) north of Greenwood. Before his departure for the Delta, Till's mother cautioned him that Chicago and Mississippi were two different worlds, and he should know how to behave in front of whites in the South. He assured her he understood.
Since 1882, when statistics on lynchings began to be collected, more than 500 African Americans had been killed by extrajudicial violence in Mississippi alone. Most of the incidents took place between 1876 and 1930; though far less common by the mid-1950s, these racially motivated murders still occurred. Throughout the South the racial caste system was predicated by whites upon avoiding interracial relationships and maintaining white supremacy. This did not prevent white men from taking sexual advantage of black women, but was meant to "protect" white women from black men. Even the suggestion of sexual contact between black men and white women carried the most severe penalties for black men. A resurgence of the enforcement of such Jim Crow mores was evident following World War II. Racial tensions increased further after the United States Supreme Court's 1954 decision in Brown v. Board of Education to end segregation in public education. Many segregationists viewed the ruling as an avenue to allow interracial marriage. The reaction among whites in the South was to constrain blacks forcefully from any semblance of social equality. A week before Till arrived, a black man named Lamar Smith was shot in front of the county courthouse in Brookhaven for political organizing. Three white suspects were arrested, but they were soon released.