In a 2001 study, university researchers attempted to come up with the total costs associated with illegal immigration incurred by U.S. counties that bordered Mexico. The researchers determined that border counties in California, Arizona, and Texas paid $108 million in court, law enforcement, and medical expenses on illegal immigrants. This money was partially reimbursed by a federal program that compensates local governments for incarcerating illegal immigrant criminals, but in 1999 these counties received only $12.4 million, or about one-eighth of their expenses. This shortfall has been criticized by local political leaders. “Counties . . . are subsidizing the federal [immigration] policies” claimed Pima County, Arizona supervisor Sharon Bronson.

The study is one of several that have attempted to ascertain the costs and benefits that illegal immigrants bring to the United States and to its taxpayers. Such studies are difficult because of the challenges of collecting data...