Brod-Posavina County recorded negative demographic trends after 1991. Negative natural change, negative net migration and population aginig have been the main demographic problems of the mentioned county for a long time. This paper presents the natural change and migration of the population in each intercensal period, ending with the 2021 census. The focus is also on the composition of the population – the biological composition in which the characteristics of the population with regard to gender and age are analyzed, the socioeconomic composition, in which the economic and educational characteristics are discussed, and the cultural-anthropological composition in which the ethnic composition of the population is presented. At the end, projection of population of Brod-posavina County until 2051 were determined, which announce the continuation of the negative demographic trend, as well as certain demographic measures that were taken to reverse such a negative demographic trend. From 1991 to 2021, the number of inhabitants of the Brod-Posavina County decreased by a little more than 25%, and more than 80% of that decrease was due to negative net migration. The share of the old population (65+) was continuously growing, as was the share of the inactive population. The ethnic composition was extremely affected by the Homeland War, the consequences of which caused a decrease in the share of the Serbian population, while the share of the Croats increased by more than 90%. Projections of the number of inhabitants until 2051 predict an additional decrease in the number of inhabitants and an increase in the share of the old population (65+).