Walsh is a former fed. prosecutor and US-German/Marshall Fund scholar on immigration, widely held out as an expert on illegal immigration.
This is basically a 2007 report based on data to 2005 so you can extrapolate from there:
Walsh's estimate of 38 million illegal aliens residing in the u.S. is calculated, however using a conservative annual rate of entry(allowing for deaths and returns to their homelands) of three illegal aliens entering the U.S. for each one apprehended. His estimate includes apprehensions at the Southern border(by far the majority),at the Northern border,Gulf Coast and at seaports and airports. Taking the DHS(Dept. of Homeland Security)average of 1.2 million apprehensions per year and multiplying it by 3 comes to 3.6 million illegal entries per year;then multiply that number by 10 for the 96-2005 period, his calculations come to 36 million illegal entries into the u.S. Add to this the approximate 2 million visa overstays during the same period, and the total is 38 million illegal aliens currently in the US.
Thanks so much. Copied and pasted, so its saved. :)