Los Angeles County is a county in California and is by far the most populous county in the United States. Figures from the U.S. Census Bureau give an estimated 2006 population of 9,948,081 residents, while the California State government's population bureau lists a January 1, 2007 estimate of 10,331,939. The county seat is the City of Los Angeles.The county is home to 88 incorporated cities and many unincorporated areas. The coastal portion of the county is heavily urbanized, though there is a large expanse of lesser populated desert inland in the Santa Clarita Valley, and especially in the Antelope Valley which encompasses the northeastern parts of the county and adjacent eastern Kern County, lying just north of Los Angeles County. In between the large desert portions of the county ― which make up around 40 percent of its land area ― and the heavily urbanized central and southern portions sits the San Gabriel Mountains containing Angeles National Forest. All of southern Los Angeles County, north to about the center of the county, is heavily urbanized.This county holds most of the principal cities encompassing the Greater Los Angeles Area, and is the most important of the five counties that make up the area. As of 2004, the county's population is larger than the populations of 42 states and is home to over a quarter of all California residents. According to the United States Conference of Mayors, Los Angeles County boasts a GDP among the twenty largest in the world.