Manzanita, Oregon. Manzanita /ˌmænzəˈniːtə/ is a coastal city in Tillamook County, Oregon, United States. It is located on U.S. Route 101 about 25 miles (40 km) south of Seaside and 25 miles (40 km) north of Tillamook. The population was 598 at the 2010 census.