Bostonia is a neighborhood located in San Diego County, California. Its geography spans two distinct jurisdictions: parts of the neighborhood are situated within the northeastern portion of the city of El Cajon, while other sections lie within an adjacent unincorporated area.
The portion of Bostonia located in the unincorporated area is classified as a census-designated place (CDP) by the United States Census Bureau. According to the 2020 census, this CDP had a population of 16,882, representing an increase from 15,379 recorded in 2010.