San Diego County, California is the fifth-most populous county by density.
 California is one of the most geographically diverse states in the union and is often geographically bisected into two regions, Southern California, comprising the ten southernmost counties, and Northern California, comprising the 48 northernmost counties
== Geography ==Covering an area of 163,696 sq mi (423,970 km2), California is the third-largest state in the United States in area, after Alaska and Texas

