Description“‘Among the Ash Heaps and Millionaires’” offers a new model for understanding the invention of greater New York. It demonstrates that city-building took place through the collective work of regional actors on the urban edge. To explain New York’s dramatic expansion between 1840 and 1940, this project investigates the city-building work of diverse local actors—real estate developers, amusement park entrepreneurs, neighborhood benefactors, and property owners—in conjunction with the work of planners. Its regional perspective looks past political boundaries to reconsider the dynamic and evolving interconnections between city and suburb in the metropolitan region. Beginning in the mid-19th century, annexed territories served as laboratories for comprehensive planning ideas. In districts lacking powerful boosters, however, amusement park entrepreneurs and summer campers turned undeveloped waterfront into a self-built leisure corridor. The systematic decision-making of local actors produced informal development plans. Estate owners disliked the crowds at nearby working-class resorts; whites blocked black access to leisure amenities. These episodes of city building, viewed together, demonstrate how local development provoked debates among competing social groups about "appropriate" regional growth and waterfront use. Progressive park planners attempted large-scale structuring of the region through beach reclamation, parks, and parkways but could not always reverse local exclusionary practices. Challenging democratic planning ideals, village governments limited public park access and property owners collectively privatized beaches. These contradictory impulses of rational growth, environmental reclamation, and exclusionary decentralization coalesced in the 1939-1940 New York World’s Fair. View comparatively, the construction of the fair and its futurist city exhibits emerge as complementary features of the re-planning and re-engineering of the modern urban environment of the 1930s. This reimagining of city-building practices calls attention to long-term environmental and urban processes, explores the dynamism of suburban environments, and brings to light the driving forces of regionalism. In aggregate, local stakeholders had the power to enhance planners’ visions of growth. But local interests could also inhibit regional planning. The contradictions inherent in collaborative city-building explain why, by 1940, New York leaders could celebrate the region’s exemplary park and highway network while simultaneously predicting the degeneration of unplanned growth into suburban sprawl.