Although the New Economic Geography (NEG) has been used extensively to formally explain the emergence of the American urban system, few studies investigate its success in explaining current population dynamics in a more established urban system. This study explores whether proximity to same-sized and higher-tiered urban centres affected the patterns of 1990-2006 US county population growth. Rather than casting NEG agglomeration shadows on nearby growth, larger urban centres generally appear to have positive growth effects for more proximate places of less than 250,000 people. However, there is some evidence the largest urban areas cast growth shadows on proximate medium-sized metropolitan areas and of spatial competition among small metropolitan areas. Copyright (c) 2009 the author(s). Journal compilation (c) 2009 RSAI.