Santa Clara County's population has grown 3.1 percent since 2010 and more than half that growth can be attributed to people who migrated to the county internationally, according to the U.S. Census Bureau.
Between April 2010 and July 2012, Santa Clara County had a net increase of 30,315 people who migrated to the county from a place other than the U.S. During the same time the county experienced a net loss of 7,029 residents who moved to another place within the U.S.
The remainder of the population increase came from 33,503 people who came the county's "natural increase," or its ratio of births to deaths. In total, the county grew by 55,862 people, from 1,781,642 to 1,837,504.
San Mateo County grew by 2.9 percent or 20,860, with just over half of the increase coming from combined international and domestic migration and the other half, some 10,156 people, coming from the county's natural increase.
San Mateo County's balance between domestic and international migration was much more modest than Santa Clara County's, with an increase of 7,364 internationally and 3,679 domestically.
The county grew from 720,105 to 739,311 people.
Neither county made the country's top-100 fastest-growing-counties list.
However, the San Francisco Metropolitan area, which includes San Francisco, Oakland and Hayward, experienced the ninth highest numeric population increase in the nation, with 58,642 people moving to the area.
The San Jose-Sunnyvale-Santa Clara metropolitan area, which includes Palo Alto, grew by 26,404 people, placing it at No. 24 in numeric population increase.