Pew Internet: A Demographic Portrait of Mexican-Origin Hispanics in the United States

A summary of trends among residents that identify themselves as Hispanic or Latino
Pew Research Hispanic Center uses Census and American Community Survey to show trends in language use and English proficiency, age, birthplace, marital status, fertility, regional dispersion, education, income, poverty status, health insurance, home ownership, and income.

From the report:

Mexicans are by far the largest Hispanic-origin population in the U.S., accounting for nearly two-thirds (64%) of the U.S. Hispanic population in 2012.1 Hispanics of Mexican origin are also a significant portion of the U.S. population, accounting for 11% overall.

Read more at: http://www.pewhispanic.org/2013/05/01/a-demographic-portrait-of-mexican-origin-hispanics-in-the-united-states

To find King County specific data: http://www.kingcounty.gov/exec/PSB/Demographics/DataReports.aspx

And to view maps of King County census data, including Hispanic/Latino, go to: http://www.kingcounty.gov/exec/equity/toolsandresources/maps.aspx