State Route 100 (SR 100) is a north–south highway in northwestern Ohio. Its southern terminus is at State Route 309 near Iberia, and its northern terminus is at State Route 53 in Tiffin.
1924 – Original route established. Originally routed from 1-mile (1.6 km) north of Brokensword to Tiffin.[2]
1939 - Extended to 12 miles (19 km) south of Bucyrus along route 19 from 1-mile (1.6 km) north of Brokensword to 3 miles (4.8 km) south of Bucyrus and an unnumbered road from 3 miles (4.8 km) south of Bucyrus to 12 miles (19 km) south of Bucyrus.[2]