It was one of 18 districts that would have voted for Joe Biden in the 2020 presidential election had they existed in their current configuration while being won or held by a Republican in 2022.

The 40th, 47th, and 49th are partitioned by Barranca Parkway, Jamboree Rd, Warner Ave, Harvard Ave, Myford Rd, Highway 5, Loma Ridge Nature Preserve, Bee Canyon Access Rd, Portola Parkway, Highway 133, Highway 241, Bake Parkway, San Diego Freeway, Ridge Route Dr, Moulton Parkway, Santa Maria Ave, Via Vista, Alta Vis, Santa Vittoria Dr, Avenida del Sol, Punta Alta, Galle Azul, Bahia Blanca W, Laguna Coast Wilderness Park, Highway S18, Aliso & Wood Canyons, Alicia Parkway, Pacific Park Dr, San Joaquin Hills Trans Corridor, Cabot Rd, San Diego Freeway, Via Escolar, Arroyo Trabuco Creek, Oso Parkway, Thomas F Riley Wilderness Park, and Ronald W Casper's Wilderness Park.

The 40th district takes in the cities of Tustin, Yorba Linda, Lake Forest, Laguna Woods, Laguna Hills, Mission Viejo, Rancho Santa Margarita, Brea, Villa Park, Aliso Viejo, eastern Orange, and eastern Anaheim, as well as the census-designated places North Tustin, Silverado, Williams Canyon, Modjeska, Trabuco Canyon and Coto de Caza.

1972 • 1974 • 1976 • 1978 • 1980 • 1982 • 1984 • 1986 • 1988 • 1990 • 1992 • 1994 • 1996 • 1998 • 2000 • 2002 • 2004 • 2006 • 2008 • 2010 • 2012 • 2014 • 2016 • 2018 • 2020 • 2022 • 2024 The seat was originally one of five reapportioned to California after the 1970 U.S. census, but its boundaries have shifted radically through successive redistricting efforts.

The district covered the cities in the northern part of the county, including Fullerton, Orange, Cypress, Stanton, and Buena Park.