The station's original call letters were KSL-FM when it began broadcasting in December 1946 as the sister station of KSL. Originally owned by the Deseret News, it became a part of Bonneville International when the LDS Church formed it as the parent of its broadcasting outlets in 1964.
"FM 100" was a pioneer of Bonneville's "beautiful music" format but in the mid-1970s it was sold to Simmons. Simmons changed the call letters in 1979 to KSFI (Simmons Family Incorporated) and began adding more vocal selections to the music mix, eventually evolving the format to soft AC. Bonneville reacquired the station (along with Star 102.7 and Arrow 103.5) from Simmons in 2003. According to the website of its owner, Bonneville International, FM100 is the top-performing adult contemporary station in Utah.