State Route 312 (SR 312) is a north–south state highway located in the southern portion of the U.S. state of Ohio. SR 312 runs from its southern terminus at a T-intersection with SR 93 approximately 4.25 miles (6.84 km) northeast of Logan to its northern terminus at a T-intersection with SR 664 nearly 1.25 miles (2.01 km) south of Bremen.SR 312 was created in the early 1930s.