County Route 18 (CR 18) is a county-maintained highway in western Otsego County, New York, in the United States. It extends for 34.83 miles (56.05 km) from an intersection with New York State Route 51 (NY 51) in the town of Butternuts to the Oneida County line at Plainfield, where it becomes CR 2. The highway runs along the eastern bank of the Unadilla River and parallels NY 8, which follows the western bank of the river. CR 18 enters the vicinity of several villages and hamlets, including the village of New Berlin and the hamlet of Unadilla Forks.

New York State Route 51 (NY 51) is a 55.02-mile-long (88.55 km) north–south state highway in the central part of the U.S. state of New York. The highway runs generally in a southwest to northeast direction from NY 8 in the hamlet of Mount Upton to north of the village of Ilion, where it ends at NY 5. NY 51 intersects several primary routes including, a short overlap with NY 23 in the village of Morris, a 2.8-mile (4.5 km) overlap with U.S. Route 20 (US 20) in Winfield, and NY 5S in Illion. NY 51 is a two-lane highway its entire length.