Route 138 is the portion of the 118-mile-long (190 km) multi-state Route 138 within the state of Connecticut. It is one of several New England state highways that travel through three states while keeping their number designation. The route begins in Sprague at Route 97. From its western terminus up to the junction with Interstate 395 in Griswold, the road functions as a collector road. From the Interstate 395 junction, it then enters Voluntown, and continues into the state of Rhode Island as Route 138.