California has the highest rate of U.S. immigrants among U.S. states, according to a new report released on June 21, 2012. U.S. immigration accounts for 27 percent of the California's population, the highest rate among U.S. states, says the report. Immigrants to California who mostly end up in filing US citizenship form along their journey also contribute 34 percent to the state's labor force and produce the same percentage of its annual GDP, or more than USD 600 billion.