In the early 20th Century New York City grew rapidly in population and developed area. The subway system grew rapidly to accommodate this new growth, but also as a concerted effort to decentralize the city away from lower Manhattan. This paper explores the co-development of the subway system and residential and commercial land uses using Granger causality models in order to determine if transit growth led residential and commercial development or if subway expansion occurred as a reaction to residential and commercial densities. The results suggest that the subway network developed in an orderly fashion and grew densest in areas where development had already occurred while lagged station densities were a weak predictor of residential and commercial densities. The implications of land use regulations and transit network density on residential and commercial land uses are discussed as are applications to contemporary planning debates.