City age and city size

There has been vast interest in the distribution of city sizes in an economy, but this research has largely neglected that cities also differ along another fundamental dimension: age. Using novel data on the foundation dates of more than 10,000 American cities, we find that older cities in the US tend to be larger than younger ones. To take this nexus between city age and city size into account, we introduce endogenous city creation into a dynamic economic model of an urban system. The city size distribution that emerges in our economy delivers a close fit to different types of US city size data. This evidence can resolve several recent debates, and build a bridge between different views in the literature on city size distributions.