Coordinates: 30°50′48″N 97°51′01″W / 30.846532°N 97.850246°W / 30.846532; -97.850246

State Highway 138, or SH 138, runs from 1.0 mile (1.6 km) north of Florence west about 6.3 miles (10.1 km) to U.S. Highway 183. The highway was originally part of SH 195. When SH 195 was redirected north of Florence to Killeen over RM 440 in 1988, this portion was redesignated as SH 138.

SH 138 was previously designated by 1933 as a short connector route in Childress County, cosigned with U.S. Highway 62. By 1939, the designation had been cancelled in favor of US 62.