Orange County Geography

According to the U.S. Census Bureau, the county has a total area of 2,455 km² (948 mi²), making it the smallest county in Southern California. Surface water accounts for 411 km² (159 mi²) of the area, 16.73% of the total; 2,045 km² (789 mi²) of it is land.

Orange County is bordered on the west by the Pacific Ocean, on the north by Los Angeles County, on the northeast by San Bernardino County, on the east by Riverside County, and on the south by San Diego County.

The northern part of the county lies on the coastal plain of the Los Angeles Basin, while the southern half lies on the foothills of the Santa Ana Mountains. Most of Orange County's population resides in one of two shallow coastal valleys that lie in the basin, the Santa Ana Valley and the Saddleback Valley. The coastal plain gently rises into the Santa Ana Mountains, which lie within the boundaries of the county and of the Cleveland National Forest. The high point is Santiago Peak (5,687 ft/1,733 m), about 20 mi (32 km) east of Santa Ana. Santiago Peak and nearby Modjeska Peak, just 200 feet shorter, form a ridge known as Saddleback, visible from almost everywhere in the county.

The Santa Ana River is the county's principal watercourse. Its major tributary running through the county is Santiago Creek. Other watercourses within the county include Aliso Creek, San Juan Creek, and Horsethief Creek. The San Gabriel River also briefly crosses into Orange County and exits into the Pacific on the Los Angeles-Orange County line between Long Beach and Seal Beach. Laguna Beach is home to the county's only natural lakes, Laguna Lakes, which are formed by water rising up against an underground fault.

The cities of Orange County are connected by a network of freeways, which residents typically call by their route number rather than their formal name (i.e., "The Fifty-five" instead of "The Costa Mesa Freeway"). One of the most important Orange County roadways is the Santa Ana Freeway, or Interstate 5, which runs North-South bisecting the length of the county. It merges with another key north-south road, the San Diego Freeway (Interstate 405) in Irvine. The 5 and 405 freeways meet at the "El Toro Y," one of the busiest interchanges in the U.S. Another notoriously busy interchange is the Orange Crush, where the 5, 22, and 57 meet.

Residents often divide the county into "North County" and "South County", as opposed to an East-West division characterized by coastal and inland cities. There is no formal geographical division of North and South County, though a North-South border may be drawn somewhere along the Tustin-Irvine and Costa Mesa-Newport Beach city boundaries, or along the boundary between the 714 and 949 area codes. Orange County is part of the five-county Greater Los Angeles area.