City age and city size

• Older cities in the US tend to be larger than younger ones.
• We introduce endogenous city creation into a dynamic economic model of an urban system.
• Model predicts a pattern of age-dependent urban growth in line with recent evidence.
• The size distribution that emerges in our economy delivers a close fit to different types of US data.
• Evidence can reconcile different views in the literature on city size distributions.

Using novel data on the foundation dates of more than 10,000 American Census places, we show 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. Our model predicts a pattern of age-dependent urban growth that is in line with recently established empirical evidence. The size distribution that emerges in our economy delivers a close fit to different types of US data and it outperforms other suggested parametrizations. This evidence can resolve several debates and build a bridge between different views in the literature on city size distributions.