A post office was established at Fiat in 1881, and remained in operation until it was discontinued in 1926. The political issue of United States Notes (fiat money) likely caused the community's name to be selected.
Jens looked at a map he'd filched from an abandoned gas station. If he was where he thought he was, he'd soon be approaching the grand metropolis of Fiat, by God, Indiana. He managed a smile when he saw that, and declaimed, "And God said, Fiat, Indiana, and there was Indiana."
--Harry Turtledove, Worldwar: In the Balance, New York:Random House (1994), Chapter 14, copyright 1994 by Harry Turtledove.