The article examines the population dynamics and ethnic composition of the population of Nakhchivan uyezd of Iravan province, which was one of the provinces of Azerbaijan during Tsarist Russia, from 1849 to 1917. Research shows that the Turkmenchay Treaty not only changed the geographical landscape of Azerbaijan, but Article 15 of the treaty had a very serious impact on the future ethnic landscape of most of its regions. Mass resettlements to the territories of the former Iravan and Nakhchivan khanates from both the Gajars and the Ottoman Empire led to demographic changes in the later Iravan province. These changes, which have manifested themselves in most parts of the province since 1850, were marked by ethnic cleansing towards the early twentieth century. In particular, the genocides committed by Armenian terrorist groups in the region in 1905-1906, as well as in the following period, led the local population to flee from one region to another. As a result, there was a sharp decline in the number of Tatars in some districts of the province, the number of Tatars, and a sharp increase in the number of foreigners and Armenians. However, Russian-language sources published in different years of the XIX-XX centuries confirm that the main ethnic group of the province, the numerical advantage, is still the Azerbaijani Turks (Tatars). We can clearly see this from the cameral notes of the central cities, uyezd centers, uyezds, districts, villages of the province, as well as the results of the census.