First settled during the Great Depression, mainly by farmers from the Dust Bowl Lincoln Acres is now an unincorporated community of San Diego County located wholly within the boundaries of the incorporated city of National City. It has a population of approximately 2,100 residents. Lincoln Acres has a fire station and library, but relies on the San Diego County Sheriff’s Department to provide police protection. Even though it has a post office, it shares its ZIP code, 91950, with National City. However the United States Postal Service lists the zip code 91947 as being located within Lincoln Acres for P.O.