Alsea is an unincorporated community in Benton County, in the U.S. state of Oregon. It is on Oregon Route 34 and the Alsea River. For statistical purposes, the United States Census Bureau has defined Alsea as a census-designated place (CDP). The census definition of the area may not precisely correspond to local understanding of the area with the same name. As of the 2010 Census, the population was 164.