The article discusses the presence of the Slovenian-speaking population in Trieste in the past and the present. After outlining the formation of the Slovenian-speaking community in the city until 1910, the article turns to the national composition of the city at the end of the Austrian era and critically analyses the results of the revised population census of that same year, based on an examination of original survey sheets for individual households in traditionally predominantly Slovenian areas. The analysis of the population survey data demonstrates that, despite Italian researchers’ insisting that it was »overly« biased towards Slovenians, the revision still failed to count the entire Slovenian population living in the city at that time. The article also critically analyses the existing data on the number of Trieste Slovenians under Italian administration and provides the author’s evaluation regarding the movement of this number between 1910 and 2015 and key reasons for the sharp decline in what was once the largest Slovenian urban community.