California's population of illegal immigrants was 2.5 million in 2009, which is 6.9 percent of the state's population and 9.3 percent of the workforce, according to a new report by the Pew Hispanic Center. The population is down from 2.6 million a year earlier but up from 2.3 million in 2000 - and 1.5 million in 2000. A weak economy is the most obvious explanation for the drop - these numbers tend to bounce around depending on job opportunities - but Pew is careful not to jump to conclusions. From the report:

The U.S. economy entered a recession late in 2007, at a time when border enforcement was increasing. Economic and demographic conditions in sending countries and strategies employed by potential migrants also change. All of these undoubtedly contribute to the overall magnitude of immigration flows. But the data in this report do not allow quantification of these factors and are not designed to explain why flows and population totals declined.

California's share of the illegal immigrant population in the U.S. has fallen sharply over the last two decades, from 42 percent in 1990 to 23 percent in 2009. That's still the biggest share of illegal immigrants in the nation, though states like Georgia and North Carolina have seen large population increases.