How do the ecosystems that support entrepreneurs form? Rather than being created through top-down actions of governments and other powerful actors, we argue that entrepreneurial ecosystems form through the everyday interactions of individuals striving to create shared meaning, resources and infrastructure needed to support their new ventures. This is especially true in ecosystems focused on creating social impact, which don’t always offer the high returns expected in a market-based capitalistic system. Our study shows how the initial activities of distributed, disparate individuals and groups rather suddenly coalesce into more coordinated, integrated and durable patterns of social interaction, creating the methods, resources and legitimacy needed for an entrepreneurial ecosystem for social impact businesses to coexist with or change existing conventions of market-based capitalism.