The United States has a long history of domestic terrorism, yet U.S. counterterrorism policy has focused almost completely on the threat from international terrorism. The gap in the literature was the absence of an empirical evaluation of U.S. counterterrorism policy on domestic terrorism in general. The purpose of this quantitative study was to describe the impact of 21st century U.S. counterterrorism policy on incidence, lethality, and cost of domestic terrorism using data from the Global Terrorism Database. The multiple streams framework and the power elite theory were used. In this longitudinal trend study using secondary data analysis, domestic terrorism data were analyzed from 749 terrorist attacks using descriptive statistics, visual analysis, and the series hazard model to examine any changes in the frequency and hazard of domestic terrorism in relation to the following 5 policies: USA PATRIOT Act, USA PATRIOT Improvement and Reauthorization Act, Animal Enterprise Terrorism Act, Implementing Recommendations of the 9/11 Commission Act, and USA FREEDOM Act. The results empirically supported the greater threat of domestic terrorism and showed that domestic terrorism changed in relation to counterterrorism policy. Further, the addition of the series hazard model in the analysis of domestic terrorism following policy implementation added additional depth to the results. This study contributed to positive social change by providing policy makers and counterterrorism agencies with an empirical, evidence-based method for evaluating U.S. counterterrorism policy and for a non-partisan, non-political, evidence-based method for quantitatively determining terrorist threat.