The numbers vary but this is about the average estimates:
"The number of illegal immigrants in the United States has grown to as many as 12 million, and they now account for about one in every 20 workers, a new estimate says. "
"It is difficult to accurately measure the number of illegal immigrants in the United States, but most public agencies and private groups had settled on a figure of about 11 million. 
The Pew Hispanic Center used Census Bureau data to estimate that the United States had 11.1 million illegal immigrants in March 2005. The center used monthly population estimates to project a current total of 11.5 million to 12 million. 
The report estimates that 850,000 illegal immigrants have arrived in United States each year since 2000"
http://www.breitbart.com/article.php...show_article=1