State Route 703 (SR 703) is a state highway in western Ohio. Its western terminus is in Montezuma at SR 219, and its eastern terminus is in St. Marys at an intersection with SR 29, SR 66, and the southern terminus of SR 116 in St. Marys. The route is mainly an east–west highway along the shores of Grand Lake St. Marys, although the section between Celina and Montezuma travels in a more north-south fashion. In 1937, the route was designated from SR 219 to US 127, and it was fully paved by 1940. SR 703 was extended to the northern side of the Grand Lake in 1973, replacing an old alignment of SR 29. Route description SR 703 travels through eastern Mercer County and the westernmost portion of Auglaize County. The busiest point in the route according to 2016 data was east of Lake Shore Drive in Celina, where the annual average daily traffic (AADT) was 16,775 vehicles. The least busy point was southeast of It's It Road, where the AADT was 1,826 vehicles. The route starts at the intersection of SR 219 and South Canal Street in the village of Montezuma, and it travels north on North Canal Street. SR 703 turns northwest at a boat ramp to Wayne Street, and travels through a small area of farmland before intersecting US 127 at a Y-intersection. The concurrency, also known as South Main Street, continues along the western banks of Grand Lake St. Marys, passing by a lighthouse as it enters the town of Celina. The road then crosses a R.J. Corman railroad and intersects SR 29 at Logan Street, which also becomes concurrent with US 127 and SR 703 briefly. At Market Street, SR 703 and SR 29 begin traveling eastward, while US 127 continues northward and SR 197 begins its concurrency with US 127. East Market Street crosses over a railroad as it leaves Celina. At Grand Lake Road, SR 703 turns south to continue as East Market Street, and SR 29 continues eastward to a divided highway. SR 703 then travels along the northern banks of the lake, with farmland north of the road. The road intersects multiple driveways and places, including the Wright State University Lake Campus and the Grand Lake St. Marys Lighthouse. Near Mercer–Auglaize County Line Road, the highway enters Auglaize County as Celina Road. The route intersects SR 364 at Koenig Road,