 The current route was originally designated on May 7, 1948 as Farm to Market Road 781 and ran from the state line to FM 703.The highway was signed, but not officially designated, concurrently as SH 128 beginning on March 30, 1955, "for guidance of traveling public" to correspond with New Mexico State Highway 128 (which was renumbered from NM 256 to NM 128 that day; FM 703 was signed but not designated as part of SH 115 in October 1952).The FM 781 designation was cancelled on August 29, 1990; the same day, FM 703 became part of SH 115.