Placentia is a city in northern Orange County, California, United States. Its population was 51,233 during the 2020 census, up from 46,488 in the 2000 census. This includes the community of Atwood, which is included in the city of Placentia, and is located in its southeastern quadrant. Primarily referred to as a bedroom community, Placentia is known for its quiet neighborhoods.

Orange County is a county located in the Los Angeles metropolitan area in Southern California, United States. As of the 2020 census, the population was 3,186,989, making it the third-most-populous county in California, the sixth-most-populous in the United States, and more populous than 19 American states and Washington, D.C. Although largely suburban, it is the second-most-densely-populated county in the state behind San Francisco County. The county's three most-populous cities are Anaheim, Santa Ana, and Irvine, each of which has a population exceeding 300,000. Santa Ana is also the county seat. Six cities in Orange County are on the Pacific coast: Seal Beach, Huntington Beach, Newport Beach, Laguna Beach, Dana Point, and San Clemente.