Orange County is a county in Southern California, United States. Its county seat is Santa Ana. As of the 2000 census, its population was 2,846,293, though a July 2008 estimate placed the population at 3,010,759, making it the second most populous county in California, behind Los Angeles County and ahead of San Diego County.

The county is famous for its tourism, the home of such attractions as Disneyland and Knott's Berry Farm, as well as several beaches along more than 40 miles (64 km) of coastline. It is also recognized for its nationally known centers of religious worship, such as Crystal Cathedral, Saddleback Church, and Calvary Chapel. It is often portrayed in the media as an affluent and politically conservative region.

Whereas most population centers in the United States tend to be identified by a major city, there is no defined urban center to Orange County. It is mostly suburban, except for some traditional downtown areas such as those of Anaheim, Santa Ana, Orange, Huntington Beach, and Fullerton. There are also several edge city-style developments such as the South Coast Metro and Newport Center.

While Santa Ana serves as the governmental center of the county, Anaheim is the main tourist destination and Irvine is the major business and financial hub. Four Orange County cities have populations exceeding 200,000: Santa Ana, Anaheim, Irvine, and Huntington Beach.

Thirty-four incorporated cities are located in Orange County; the newest is Aliso Viejo, which was incorporated in 2001. Anaheim is the oldest, incorporated in 1870 when the region was still part of neighboring Los Angeles County.