Although the literature on accelerators, an important and newer model of entrepreneurial support, considers their performance and the definition of the form, little is known about how accelerators populate in a single ecosystem over time. We find accelerators are established by different types of entities such as non-profit organizations, local governments, universities, and even foreign government agencies with different goals. Based on a novel dataset of all 107 accelerator programs that ever operated in New York City, we propose a new way of categorizing accelerators by their founding attributes. We confirm that the emergence of accelerators in New York City started with the entry of non-profit accelerators for the purpose of local economic development. For-profit actors followed. Accelerators began from the periphery of the city’s geographic boundaries, but over time became concentrated in Manhattan. We also observe a shift toward sector specialization. Our contributions are to examine the development of one entrepreneurial support organization over time in one ecosystem, present a method to categorize accelerators based on their sub-niches, and to provide evidence of a catalyzing role of local government in fostering ecosystem emergence.