We develop a duocentric-city model and show that the ratio between the property tax in the suburbs and in the center has an ambiguous impact on the size of the city. We test this model by using a dataset of effective property tax rates which we developed using GIS techniques for central cities and suburbs in 445 urbanized areas. Results from the empirical analyses suggest that a lower property tax rate in the suburbs as compared to the central city is associated with more expansive urban growth and a greater level of decentralization of population and employment.