State Route 73 (SR 73) is an east–west state highway in the southern portion of the U.S. state of Ohio. Its western terminus is on U.S. Route 27 in Oxford at the intersection of SR 732. SR 73's eastern terminus is in Portsmouth at US 23; this is also the southern terminus of SR 104, and the two state routes run concurrently for over 6 miles (9.7 km) from this point north. Once SR 73 enters Scioto County, it is designated as the Scenic Scioto Heritage Trail by the Ohio Department of Transportation.^[2]

In combination with SR 32, SR 73's easternmost 31 miles (50 km) are part of the quickest route between Cincinnati and Portsmouth.

The portion of SR 73 between Interstate 75 and SR 741 in Springboro is designated as the "Officer Bill Johnson Memorial Highway",^[3] in honor of William L. "Bill" Johnson, a 48-year-old, eight-year veteran of the Springboro Police Department who was struck and killed by a vehicle around 12:30 a.m. on June 27, 1983, while outside his cruiser on SR 73, investigating two people walking in the roadway.^[4]

• Great Miami River - Middletown, Franklin
• Excello Locks - Historic Remains of a lock on the Miami-Erie Canal near the intersection of 73 and S. Main St. in Middletown, Ohio. Much of the route between Trenton and Franklin follows the original path of the Miami and Erie Canal.
• Middletown Historical Society Canal Museum
• Springboro Historic District - Springboro at SR 741.
• La Comedia Dinner Theatre - Springboro
• Little Miami River - Waynesville
• Little Miami Bike Trail - Corwin
• Caesar Creek Lake - Warren County
• Caesar Creek State Park - Warren, Clinton County
• Serpent Mound
• Brush Creek State Forest
• Shawnee State Forest
• Scioto River
• Ohio River

• 1924 – Original route established;^[5] originally routed from Franklin to 1-mile (1.6 km) west of Portsmouth (dually certified with State Route 104 from 1-mile (1.6 km) north of Coles Park to 1-mile (1.6 km) west of Portsmouth before 1926).^[6]
• 1926 – Extended to 2 miles (3.2 km) east of Middletown along the previous State Route 6; State Route 104 certification removed.^[6]
• March 9, 1932 – Extended to the U.S. Route 127 about 1-mile (1.6 km) northwest of Seven Mile.^[7]
• 1936 – Extended to Oxford.^[6]
• 1952 – Dually certified with State Route 104 from 1-mile (1.6 km) north of Coles Park to 1-mile (1.6 km) west of Portsmouth.^[6]
• 1957 – From Excello to Franklin upgraded to 4 lanes.^[6]
• 1962 – From 1-mile (1.6 km) north of West Portsmouth to 1-mile (1.6 km) west of Portsmouth upgraded to 4 lanes.^[6]
• 1966 – From Franklin to Interstate 75 upgraded to 4 lanes.^[6]
• 1972 – Extended to Portsmouth (dually certified with State Route 104)^[6] along the former alignment of U.S. Route 23.
• 1979 – From Interstate 75 to Springboro upgraded to divided highway.^[6]
• 1980 – From Trenton to Excello upgraded to divided highway.^[6]
• 2011 – Realigned around Wilmington along a new bypass.^[8]

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