(with Ruben Enikolopov, Gianluca Russo, David Yanagizawa Drott)

Online social networks have changed how people interact across large distances. We examine the long-run effect of a key feature of these networks - online homophily - on interpersonal interactions in local communities. Using Facebook data, we measure online homophily across counties in the United States. To identify effects, we exploit a conflict between Facebook and Google in the early expansion phase of Facebook, which induced persistent variation in online homophily across counties. Using various measures of both online and offline behavior, we find evidence that local social interactions have been affected. In particular, homophilic connections made people use Facebook more often but socialize less offline, as measured through bar and restaurant visits. Individuals have also become less connected across income strata. Political opinions within counties became more diverse, with a lowered probability that two voters in a county support the same political party. Overall, our results indicate that when a natural demand for connecting with socially similar people is met by the supply of a `death-of-distance' technology, it comes at the cost of short-distance social cohesion.