The route became a state highway in 1930, running 9.9 miles (15.9 km) from Highway 4 south to McGehee, with Highway 4 running east to Tillar. Prior to 1940, Highway 4 was rerouted onto the former Highway 138, with the former routing to Tillar becoming Highway 138. This change is still apparent on the highway map, as Highway 4 was later replaced by US 278, which creates today's "kink" in US 278 in east Drew County. The routing of today's Highway 138 appears on the state highway maps beginning in the mid–1950s, but is not numbered. Around 1960, a segment from Winchester to Kelso becomes Highway 138, in addition to a segment from Tillar north to Winchester. The Kelso segment was redesignated Arkansas Highway 277 in the mid-1960s, which enabled a contemporaneous extension of Highway 138 from Winchester west to the current Highway 293. By 1966, the route was extended to Monticello. The road was paved from Monticello north in 1967, as the segment between US 65/US 165 and Kelso was paved upon its earlier designation.
^ abcdPlanning and Research Division (2010). "Arkansas Road Log Database" (Database). Arkansas State Highway and Transportation Department. Archived from the original on 23 June 2011. Retrieved June 9, 2011.