The 1940 Iowa State Senate elections took place as part of the biennial 1940 United States elections.

A statewide map of the 50 state Senate districts in the 1940 elections is provided by the Iowa General Assembly here.

The primary election on June 3, 1940, determined which candidates appeared on the November 5, 1940 general election ballot.

To claim control of the chamber from Republicans, the Democrats needed to net 14 Senate seats.

Republicans maintained control of the Iowa State Senate following the 1940 general election with the balance of power shifting to Republicans holding 45 seats and Democrats having 5 seats (a net gain of 7 seats for Republicans).