Sigh. If the New York times keeps publishing these fantastic interactive maps, I'm going to have to keep posting them.
This one depicts immigrant communities in the US in typical Timesian detail: with the biggest contributor to and population of the immigrant commnities in every single county in the country, and for every decade going back to 1880.
There are also maps showing the distribution of immigrant groups across the country, like this one showing population born in Mexico by county.
The Times map lets you mouse over the bubbles to see county and immigrant populations for every dacade.