Formerly, from 2003 to 2013, the 21st district covered all of Tulare County and the eastern half of Fresno County. As of 2022, it is the most Democratic district to be represented by a Republican.
According to the APM Research Lab's Voter Profile Tools (featuring the U.S. Census Bureau's 2019 American Community Survey), the district contained about 377,000 potential voters (citizens, age 18+). Of these, 63% are Latino, while 26% are White. Immigrants make up 16% of the district's potential voters. Median income among households (with one or more potential voter) in the district is about $51,500, while 15% of households live below the poverty line. As for the educational attainment of potential voters in the district, 23% of those 25 and older have not earned a high school degree, while 12% hold a bachelor's or higher degree.
As of the 2020 redistricting, California's 21st congressional district is located in the San Joaquin Valley. It encompasses central Fresno County and the northwestern part of Tulare County.
Fresno County is split between this district, the 5th district, the 13th district, and the 20th district. The 21st and 5th are partitioned by N Willow Ave, E Herndon Ave, E Bullard Ave, N Blackstone Ave, W Shaw Ave, Burlington Northern Santa Fe, N Marks Ave, N Hazel Ave, W Figarden Dr, and W Herndon Ave. The 21st and the 13th are partitioned by N Dickenson Ave, Highway 180, S Garfield Ave, W California Ave, S Grantland Ave, W Jensen Ave, S Chateau Fresno Ave, W North Ave, W American Ave, S Westlawn Ave, W Lincoln Ave, Shayes Ave, W Sumner Ave, S Cornelia Ave, W South Ave, S East Ave, E Mountain View Ave, S Sunnyside Ave, E Clemenceau Ave, S Fowler Ave, E Elkhorn Ave. The 21st and 20th are partitioned by E Bullard Ave, N 4th St, E Browning Ave, N Millbrook Ave, E Barstow Ave, N Cedar Ave, E Rialto Ave, E San Gabriel Ave, N Maple Ave, Dry Creek, E Dakota Ave, N Chestnut Diagonal, E Pontiac Way, N Ann Ave, W Dakota Ave, N Clovis Ave, E Dayton Ave, Duke Ave, N Duke Ave, E Shields Ave, N Miami Ave, E Princeton Ave, E Brown Ave, N Fordham Ave, E Clinton Ave, San Joaquin Valley, E Belmont Ave, N Temperance Ave, S Temperance Ave, E Central Ave, S Del Rey Ave, S Indianola Ave, Highway 180, S Academy Ave, E Switch Ave, E California Ave, S Rainbow Ave, S Riverbend Ave, E Annadale Ave, S Reed Ave, and Friant Kern Canal. The 21st district takes in the cities of Fresno, Selma, Reedley, Parlier, Orange Cove, and Sanger.
Tulare County is split between this district and the 20th district. They are partitioned by Boston Ave, N 4th Ave, Excelsior Ave, San Joaquin Valley, Road 56, Highway 198, N Camp Dr, N Neeley St, S Plaza St, Highway J19, Highway J32, N Hall Ave, Highway 63, W Tulare Ave, E Mineral King Ave, E Noble Ave, Avenue 296, Road 156, N Mariposa Ave, Avenue 264, W Myer Ave, San Joaquin Valley, E List Ave, Rocky Hill Dr, Avenue 280, Yokohl Dr, Palm Dr, Fritz Dr, Road 248, Dry Creek Dr, Avenue 360, Road 212, Highway 245, Millwood Dr, Friant Kern Canal, Negro Creek Rd, and Sand Creek. The 21st district takes in the north side of the city of Visalia, as well as the cities of Dinuba, Farmersville and Exeter.