The INS thinks - ahem - there are 1 million people crossing the Mexian border illegaly evey year. Others say the number is about 1.5 million. Last week I heard a report on the radio that said the number is 3 million.
I don't think anybody really knows, but after a few years the real numbers do come in when people have to get some kind of legal papers.
According to one analysis it is estimated that in 20 years Latinos will be the largest ethnic community in the USA.