This paper discusses the one-city monopoly phenomenon in Turkey from 2007 to 2018 from inequality. For this purpose, Theil Inequality Index is calculated for the NUTS3 level, and a significant gap between İstanbul and other cities is obtained. Then, club convergence analysis and clustering procedure are applied. According to the finding, the overall country’s convergence hypothesis is rejected, and 75 of 81 cities have converged into six clubs. In these heterogeneous convergence clubs, İstanbul has confirmed the one-city monopoly characteristics while diverging from others, both in its great strength and the risks the city confronts.