Upon being sentenced, Gacy was transferred to the Menard Correctional Center in Chester, Illinois, where he remained incarcerated on death row for 14 years. Isolated in his prison cell, Gacy began to paint. The subjects Gacy painted varied, although many were of clowns, some of which depicted himself as "Pogo". Many of his paintings have been displayed at exhibitions;[298][299] others have been sold at various auctions, with individual prices ranging between $200 and $20,000.[300] Although Gacy was permitted to earn money from the sale of his paintings until 1985, he claimed his artwork was intended "to bring joy into people's lives"
On the morning of May 9, 1994, Gacy was transferred from the Menard Correctional Center to Stateville Correctional Center in Crest Hill to be executed. That afternoon, he was allowed a private picnic on the prison grounds with his family. For his last meal, Gacy ordered a bucket of Kentucky Fried Chicken, a dozen fried shrimp, french fries, fresh strawberries, and a Diet Coke. That evening, he observed prayer with a Catholic priest before being escorted to the Stateville execution chamber to receive a lethal injection. According to published reports, Gacy was a diagnosed psychopath who did not express any remorse for his crimes. His final statement to his lawyer before his execution was that killing him would not compensate for the loss of others, and that the state was murdering him. His final spoken words were "Kiss my ass."