On Friday, the Pew Research Center’s Forum on Religion & Public Life released its analysis on the religious affiliation of immigrants to the United States.
When it comes to legal immigrants who are religiously unaffiliated — atheists, agnostics, and those who may be spiritual-but-not-religious — the estimates are pretty steady:

In 1992, an estimated 130,000 new permanent residents had no religious affiliation. The estimate for 2012 is 140,000.
Since 1992, the U.S. has admitted nearly 2.8 million religiously unaffiliated legal permanent residents. By comparison, the U.S. population in 2010 included more than 40 million people with no religious affiliation.
And where are they all coming from? Mostly from the Asia-Pacific region:

More than half come from countries in the Asia-Pacific region, including China and Vietnam. About a quarter come from nations in the Americas, such as Mexico and Canada. Another significant share of unaffiliated immigrants were born in Europe, although that percentage has decreased since 1992.
Nearly two-thirds of all immigrants are Christians — no surprise there — but it’s a slight decrease from 20 years ago. The percentage of Muslims and Hindus, though, has gone up, offsetting the percentages.
Pew is careful to note that these numbers are all estimates based on government statistics and self-identification surveys of new immigrants.
Much like with the increase in Hispanic atheists, the results suggest that the atheist community at large would be wise to reach out to people who fall outside our traditional demographics, people who may not believe in God but have no outlet for their thoughts on religion.