It is generally accepted that fiscal decentralization increases citizens’ control over politicians, fostering accountability and increasing efficiency. This article identifies the socioeconomic characteristics of citizens (potential voters) that increase their control over local policy-makers and thus generate greater efficiency in a decentralized context. We also highlight the fiscal characteristics of local governments that influence this control and efficiency. The study examines a sample of Spanish municipalities, applying a methodology based on the conventional procedure of two-stage estimation. In the first stage we estimate the efficiency of local public services by calculating a new version of a global output indicator using the DEA technique. In the second stage, using a Tobit type estimation (censored models) and bootstrap methods, we show how the factors mentioned may influence efficiency. The results suggest that strong presence of retailers, retired people, and people entitled to vote favour citizens’ control, which fosters accountability and efficiency. A factor that facilitates this control, and therefore greater efficiency, is the presence of low opportunity costs for obtaining information regarding local public service management.