 On March 19, 1949, a southern section of FM 400 was designated, replacing FM 1074.This southern section was in Lynn County, and ran southward from the Lubbock County line through Wilson to US 87.This created a gap in the routing of FM 400 in and around Slaton; this gap would be closed on May 23, 1951, when the two sections of FM 400 were both extended to connect with US 84 at two different points in Slaton.