A map of estimated illegal immigrant population, state by state. ~snip~ Estimating where exactly illegal immigrants reside in the United States is tricky, but the Pew Hispanic Center did just that in 2011 for each state. Although California has the highest number of illegal immigrants, Nevada has the largest proportion of illegal immigrants—7.2 percent of the state population and as much as 10 percent of its workforce. California and Texas follow at just under 7 percent of their populations, with New Jersey and Arizona rounding out the top five. ~snip~