The 1885 United States Senate election in Illinois was held from February 18 to May 19, 1885. The contentious election was determined by a joint session of the Illinois General Assembly. Incumbent RepublicanUnited States SenatorJohn A. Logan, seeking a third term (second consecutive) in the United States Senate, was unanimously nominated by a Republican caucus. However, some assemblymen expressed concern about the candidate and abstained from supporting him.
Logan initially faced off against DemocratWilliam Ralls Morrison, who was nominated during a legislative session. When the election began on February 18, the assembly combined for 102 Republicans and a coalition of 102 supporting the Democrats, thus producing a stalemate. For the next two months, elections were held to no avail during joint sessions. On April 12, a Democratic representative died and a Republican candidate won the special election to replace him. This angered Democrats, who tired of Morrison's lack of appeal and nominated Judge Lambert Tree in his place. After three months, the last Republican holdout consented to follow the rest of his party, and Logan was elected with 103 of the 204 votes.