A Chicago man who spent 32 years behind bars before DNA evidence helped overturn his conviction for the rape and murder of a three-year-old girl has been released from prison.

The Illinois department of corrections said 50-year-old Andre Davis had left the super-maximum security prison in Tamms in far southern Illinois at about 7.30pm on Friday, hours after the local state's attorney agreed to drop the case against him.

An Illinois appeals court ordered a new trial in March. Tests found that DNA taken from the scene of the 1980 killing of Brianna Stickle in Rantoul was not his.

According to the Center on Wrongful Convictions at Northwestern University, Davis is among 42 former inmates who have been exonerated by DNA evidence in Illinois. Of those, he served the most time behind bars.