Research Summary We develop a set of hypotheses informed by a social disorganization framework and test them using newly available data on nearly 600 terrorist attacks in U.S. counties from 1990 to 2011. Our results show that terrorist attacks were more common in counties characterized by greater language diversity, a larger proportion of foreign‐born residents, greater residential instability, and a higher percentage of urban residents. Contrary to the social disorganization perspective but in keeping with most prior research, terrorist attacks were less common in counties marked by high levels of concentrated disadvantage. More generally, we found steady declines in the number of terrorist attacks on U.S. soil from 1990 to 2011. We discuss the implications of the results for theory, future research, and policy. Policy Implications Terrorism, like ordinary crime, is highly concentrated. Of the 3,144 counties in the United States, only 250 (7.95%) experienced a terrorist attack from 1990 to 2011; 5 counties (0.002% of total U.S. counties) accounted for 16% of all attacks. Moreover, counties at greatest risk of terrorist attack have identifying characteristics. Just as random preventive patrol policing has generally been replaced by more targeted strategies, efforts to counter terrorism might benefit from strategies that target certain counties: those with high population heterogeneity and great residential instability that are highly urban. And just as targeting particular neighborhoods raises equity concerns in policing, policies aimed at counties with particular characteristics pose a challenge for countering terrorist attacks. However, unlike the situation in policing ordinary crime, high‐terrorism‐risk counties are generally not characterized by economic disadvantage or a large proportion of racial and ethnic minorities.