Necanicum is an unincorporated community in Clatsop County, Oregon, United States. It is located approximately 13 miles southeast of Seaside on U.S. Route 26 in the Northern Oregon Coast Range, next to the Necanicum River. Necanicum Junction is about a mile east of the site of the former post office, at the intersection of U.S. 26 and Oregon Rout…Necanicum is an unincorporated community in Clatsop County, Oregon, United States. It is located approximately 13 miles southeast of Seaside on U.S. Route 26 in the Northern Oregon Coast Range, next to the Necanicum River. Necanicum Junction is about a mile east of the site of the former post office, at the intersection of U.S. 26 and Oregon Route 53. It is served by the Seaside post office.