State Fair is a 1945 American Technicolor musical film directed by Walter Lang, with original music by Rodgers and Hammerstein. It is a musical adaptation of the 1933 film of the same name starring Janet Gaynor and Will Rogers. The 1933 film is an adaptation of the 1932 novel by Phil Stong. This 1945 musical film stars Jeanne Crain, Dana Andrews, Dick Haymes, Vivian Blaine, Fay Bainter, and Charles Winninger. State Fair was remade in 1962, starring Pat Boone and Ann-Margret.

State Fair is the only Rodgers and Hammerstein musical written directly for film. The movie introduces such popular songs as "It's A Grand Night For Singing" and "It Might as Well Be Spring", which won the Academy Award for Best Original Song. Joint musical direction by Alfred Newman and Charles E. Henderson is of orchestral arrangements principally composed by Edward B. Powell.

This Rodgers and Hammerstein's original musical film was later adapted for the stage in 1969, for a production at The Muny (St. Louis Municipal Opera Theatre), a landmark amphitheatre in St. Louis, Missouri. In 1996, it was adapted again for a Broadway musical of the same name, with additional songs taken from other Rodgers and Hammerstein musicals.