Seaside is a city in Clatsop County, Oregon, United States, on the coast of the Pacific Ocean. The name Seaside is derived from Seaside House, a historic summer resort built in the 1870s by railroad magnate Ben Holladay. The city's population was 6,457 at the 2010 census.

Clatsop County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 41,072. The county seat is Astoria. The county is named for the Clatsop tribe of Native Americans, who lived along the coast of the Pacific Ocean prior to European settlement. Clatsop County comprises the Astoria, OR Micropolitan Statistical Area, or Sunset Empire, and is located in Northwest Oregon.