Pew Research Center has a massive new study out on immigration to the US. One part of the study looked at birth regions for recent immigrants using Census data.
Immigration from Mexico steadily rose between 1970 and 2000. By the latter year, about 2.6 million immigrants who had moved to the US within the previous five years came from Mexico. Over the next decade and in the wake of the Great Recession, however, immigration from Mexico plummeted. By 2013, just over 900,000 immigrants had come from Mexico over the past three years.
Meanwhile, immigration from Asia continues to steadily grow. In 2000, about 1.9 million Asians had immigrated to the US in the previous five years. By 2013, that number grew to just under 2.5 million, making Asia by far the biggest recent source of immigrants to the US.
The study contains many more interesting details on immigrants, and you can see the full study at Pew's website.