13 million illegal aliens: A recent study at Northeastern University in Boston by researchers Andrew Sum, Neeta Fogg, and Paul Harrington concludes as many as 13 million illegal aliens may reside in the United States. This is comparable in size to the combined populations of the following 13 states and the District of Columbia (in alphabetical order): Alaska, Delaware, Hawaii, Idaho, Maine, Montana, Nebraska, New Hampshire, North Dakota, Rhode Island, South Dakota, Vermont, Wyoming, and the District of Columbia; total population of 12,588,161 in the 2000 census. See itemized listing. The U.S. Immigration and Naturalization Service says about 40% of the illegal aliens are in California. The 2000 census counted about 8 million undocumented illegal aliens in the United States, and expert demographers admit it may have missed some.