This paper contributes to identify determinants of social media adoption by local governments and of the audience they reach through that channel, after adoption. The 43 districts of Lima, the capital city of Peru, were used as a case study. Primary data about the presence and audience of these local governments on Facebook, Twitter, and YouTube was collected to support the analyses. Main conclusions are that socioeconomic dynamism and previous experience in implementing e-government are relevant determinants of both adoption and audience; and that population size is a relevant determinant of audience but not a relevant determinant of adoption. These results contribute to the theory by further validating and complementing results that were previously obtained in other Latin-American countries and in other regions in the world.