Local governments increasingly confront policy problems that span the boundaries of individual political jurisdictions. Institutional theories of local governance and intergovernmental relations emphasize the importance of networks for fostering service cooperation among local governments. Yet empirical research fails to examine systematically the effects of social networks on interlocal service cooperation. Do the individual networks of local government actors increase their jurisdiction's level of interlocal service delivery? Drawing data from the National Administrative Studies Project IV (NASP-IV), multivariate analysis is applied to examine this question among 919 municipal managers and department heads across the United States. The findings indicate that interlocal service cooperation increases when jurisdictional actors network frequently through a regional association or council of government and when they are united by a common set of professional norms and disciplinary values. Manager participation in professional associations, however, does not increase interjurisdictional cooperation. The key conclusion for local government practitioners searching for ways to increase collaboration: networks that afford opportunities for more face-to-face interaction yield better results for effective service partnerships.