Ohio State Route 821

State Route 821 (SR 821) is a north–south state highway in the southeastern portion of the U.S. state of Ohio. A state-maintained section of the old US 21, its southern terminus is at SR 60 approximately 2 miles (3.2 km) north of Marietta, and its northern terminus is at I-77 in Byesville, along with the eastern terminus of SR 209. The route is entirely undivided surface road, and is much less direct than the newer I-77 which supplanted it as a through route. As the interstate was being built, the designation of US 21 was moved to the freeway before Ohio wholly decommissioned the now-superfluous U.S. route. SR 821 was designated about two years after US 21 was moved onto I-77 in southeastern Ohio.