This thesis examines the demographic development of the Osječko-baranjaska County in the period from 2001 to 2021, using data from the last three population censuses. The first part of the paper focuses on the analysis of demographic trends, including the number and distribution of the population, population density, migration, and population circulation. The data was processed using Microsoft Office Excel and ArcGIS software, specifically the ArcMap 10.4.1 application. Observing the demographic changes in the Osječko-baranjska County from 2001 to 2021, a significant population decline in administrative cities and municipalities is evident, with the county’s population decreasing by nearly 13% between 2011 and 2021. The natural increase has been consistently negative, with particularly high mortality rates in 2020 and 2021, which can be linked to the COVID-19 epidemic and population aging. Migration trends also show emigration patterns, especially among young people, a phenomenon that intensified after Croatia's entry into the European Union. The county’s population is characterized by rapid aging, with a marked decrease in the share of young people and an increase in the share of older individuals. Aging indices and dependency ratios show significant changes in the population structure, with rural municipalities being particularly affected by demographic aging and depopulation.