We investigate the relationship between neighboring municipal authorities’ shared party affiliation and inter-jurisdictional cooperation agreements in Mexico. Exploiting a Regression Discontinuity Design in close municipal elections, we show that political alignment with neighboring municipalities translates into higher levels of inter-jurisdictional cooperation. Focusing particularly on crime prevention, we then document that cooperation has observable returns (homicide rates decline significantly) and that the difference in the probability of observing a cooperation agreement between same and different party mayors is larger when the returns to cooperation are higher.