Scholars and practitioners agree that homeland security policy implementation is contingent on a strong system of intergovernmental relations. The responsibilities associated with the homeland security mission, often mandated, cut across federal, state, and local boundaries. Local-level stakeholders are especially important players in the implementation process. This article presents a local perspective on the way intergovernmental relations have changed—and the reasons for those changes—since 9/11. Results of a survey of county and city officials in Florida provide evidence that intergovernmental cooperation has improved as a result of federal and state mandates. These results are refined by an analysis of the effects of specific local characteristics and the quality and quantity of vertical and horizontal networks on intergovernmental cooperation and local preparedness. Homeland security appears to be a policy area in which mandated cooperation and coordination—in a time and place of urgency—have actually strengthened the intergovernmental system.