This article uses immigration and other biographical data to refute much of the conventional wisdom about the relationship between terrorism and immigration. Using a database created from the biographical data of 373 terrorists, we have established a number of significant findings. Over forty percent of our database is made up of Western Nationals. Second, despite widespread alarms raised over terrorist infiltration from Mexico, we found no terrorist presence in Mexico and no terrorists who entered the U.S. from Mexico. Third, we found a sizeable terrorist presence in Canada and a number of Canadian-based terrorists who have entered the U.S. In addition to illuminating the terrorist networks entrenched in the West, this paper is also an attempt to advance the field of terrorism studies by taking a quantitative approach to data analysis.