Cities and CDPs in the district included Castro Valley, Dublin, Hayward, Livermore, Pleasanton, Sunol, and Union City; most of San Ramon; and parts of Danville and Fremont.

As of the 2020 redistricting, California's 15th congressional district is part of the San Francisco Bay Area.

They are partitioned by the San Francisquito Creek, Menalto Ave, Willow Rd, S Perimeter Rd, W Perimeter Rd, Bay Rd, Marsh Rd, Middlefield Rd, Highway 82, Highway 84, Alameda de las Pulgas, Woodhill Dr, Farm Hill Blvd, The Loop Rd, Jefferson Ave, Summit Way, California Way, Junipero Serra Freeway, and Highway 35.

The 15th district takes in the northern portions of the town of Atherton and city of Menlo Park, the cities of San Mateo, Daly City, South San Francisco, Redwood City, Burlingame, San Bruno, Millbrae, East Palo Alto, San Carlos, Foster City, Belmont, Brisbane, the towns of Hillsborough and Colma, as well as the census-designated places North Fair Oaks, Broadmoor, Highlands, Baywood Park, and Emerald Lake Hills.

Along with San Mateo County, the 15th district also takes in the San Francisco neighborhoods of Crocker Amazon, Excelsior, Little Hollywood, Mission Terrace, Oceanview, Outer Mission, Portola, and Visitacion Valley.