While the scholarly literature largely ignores issues of suburban population size, density and heterogeneity, during the 1920s a number of large, densely-settled, heterogeneous suburbs emerged on the fringe of the largest US cities. The article identifies forty-one of these potential ‘city suburbs’ which are defined as communities having minimum thresholds of 25,000 population and residential densities of 6,000 per square mile. City suburbs may have claimed nearly 25 per cent of the suburban populations of the nation's ten largest metropolitan districts. Drawing largely on data for midwestern cities, city suburbs are further identified through their diverse populations by class, ethnicity and race; varied housing stocks and economic activities including retailing, professional services and manufacturing; and political independence from their central city. Nearly equally divided between residential and industrial suburbs, the former, including Oak Park, Illinois, ‘fit’ traditional middle-class suburban descriptions while neighbouring Cicero represented workingclass, industrial communities.