Fallbrook is an unincorporated census-designated place in northern San Diego County, California, United States. The community had a population of 32,267 at the 2020 United States census, making it one of the largest unincorporated communities in the county. Fallbrook lies immediately east of Marine Corps Base Camp Pendleton and is widely known for its avocado groves; the community styles itself the "Avocado Capital of the World" and hosts an annual Avocado Festival on Main Avenue.