Live in Cook County Jail is a 1971 live album by American blues musician B.B. King, recorded on September 10, 1970, in Cook County Jail in Chicago. Agreeing to a request by jail warden Winston Moore, King and his band performed for an audience of 2,117 prisoners, most of whom were young black men. King's set list consisted mostly of slow blues songs, which had been hits earlier in his career. When King told ABC Records about the upcoming performance, he was advised to bring along press and recording equipment.

Live in Cook County Jail spent thirty-three weeks on the Billboard Top LPs chart, where it peaked at number twenty-five. It also reached number one on the Top R&B chart, King's only album to do so. In addition to positive reviews from critics, much of the press surrounding Live in Cook County Jail focused on the harsh living conditions in the prison, which led to an eventual reform.

Although Live in Cook County Jail continues to receive praise as one of King's best albums, critics often overlook it in favor of 1965's Live at the Regal. Rolling Stone ranked Live in Cook County Jail at number 499 on its list of the 500 Greatest Albums of All Time, and in 2002, it was inducted into the Blues Foundation Hall of Fame. The performance at Cook County Jail had a profound impact on King, who not only continued to perform free concerts at prisons throughout his life, but also co-established the Foundation for the Advancement of Inmate Rehabilitation and Recreation.

The warden of Cook County Jail, Winston Moore, approached King after a 1970 performance at the popular Chicago nightclub Mister Kelly's and asked him to perform for the prisoners at the jail. As King recalled: "He said to me, 'It's a first for you at Mister Kelly's and it's a first for me as a black person over here, so why don't we both get together and do another first and get you to play for the inmates?' That's how it came about." King agreed, and politician Jerry Butler (former singer for the Impressions) helped to arrange a special free concert at the jail. Recordings of prison concerts were becoming popular around this time, as indicated by At Folsom Prison by Johnny Cash. Biographer Sebastian Danchin [fr] noted this performance was not to cash in on this craze however, but instead was to deliver hope. "The prisoners saw King's visit as an all-too-rare recognition of their humanity" wrote Danchin.

When King told his record label ABC Records that he was going to perform at Cook County Jail, label executives told him to bring along the press and recording equipment. King and his backing band were given a personalized tour of the prison, and were taken through the mess hall and hallway of cells. The musicians felt uncomfortable while walking through the prison; pianist Ron Levy described the stares from the prisoners as "hauntingly hollow". The musicians were given a small stage in the courtyard, while the prisoners were given hundreds of folding chairs.

Live in Cook County Jail was recorded on the afternoon of September 10, 1970. King's backing band consisted of: Levy on the piano, John Browning on the trumpet, Louis Hubert on the tenor saxophone, Brooke Walker on the alto saxophone, Wilbert Freeman on the bass guitar, and Sonny Freeman on the drums. The crowd consisted of 2,117 prisoners, who were required to sit through the performance. Prisoners who wanted to dance were allowed to stand toward the back of the yard. Around 80% of the prisoners attended the performance, while the rest stayed in their cells. King estimated around 70 to 75% of the prisoners were black or of other minority races, and were either in their late teens or early twenties. Prison officials hired additional security for the event, mainly retired boxers.

Live in Cook County Jail opens with a female official introducing members of the prison administration. A light applause is quickly followed by loud booing. The official then introduces King and his backing band, who begin to play a brief, fast tempo version of "Every Day I Have the Blues". The rest of the setlist in Live in Cook County Jail features slow blues tracks, with lyrical themes of separation and loneliness. King occasionally has conversations with the audience, such as on "Worry, Worry, Worry", where he tells the audience that men and women are God's gift to each other. Biographer David McGee describes these conversations as "a classic bit of bluesman as evangelist or soothsayer".

The setlist in Live in Cook County Jail favors King's early hits – songs which had been in his live repertoire since the 1950s. "3 O'Clock Blues", "Darlin' You Know I Love You", and "Every Day I Have the Blues" were important hits early in his career, while "Please Accept My Love", "Worry, Worry, Worry", and "Sweet Sixteen" date from 1958 to 1960. The sole contemporary song, 1969's "The Thrill Is Gone", became one of King's biggest hits in recent years. Author Ulrich Adelt believes the setlist was chosen to elicit the feeling of nostalgia from the primarily black audience. To record the performance, producer Bill Szymczyk hired Aaron Baron, the owner of a company called Location Recorders, to record the show from a remote truck. Baron then gave Szymczyk the tapes to be mixed.