The Chicago Democrat had filed petitions for both the congressional race and the county election. Monday is the deadline to drop out of one of the races.
Davis tells The Associated Press that he decided to seek re-election because he and three other black candidates running in the Cook County race would have competed for the same base of voters. He says he'll give further details at a news conference later in the morning.
Davis was first elected to Congress in 1996. The 7th district includes downtown Chicago and some western suburbs.