Other studies suggest that children of Spanish-speaking immigrants are increasingly likely to also speak English as they come up through the American public school system.

The census report said 30 percent of Texans in 2007 were speaking Spanish in their homes, an increase of 3 percentage points from 2007. In the Dallas-Fort Worth area, 1.3 million people spoke Spanish in 2007, compared with 890,000 in 2000.

The increases come at a time when 12 percent of the U.S. population was born outside of the country. A third of those, or 12 million people, were born in Mexico.

The U.S. Census Bureau reported that one out of five people speak Spanish in Arizona, California, New Mexico and Texas.