The graduate thesis titled „The Population of Karlovac Based on the Death Register of the Holy Trinity Parish in the 18th Century“ explores the demographic characteristics of Karlovac using death registers from the Holy Trinity Parish in two periods of the 18th century: 1730-1739 and 1760-1769. The research focuses on depicting the population structure and social aspects through a detailed analysis of the register entries. The thesis is divided into two main sections. The first section provides a historical overview of the development of Karlovac, including its founding, strategic significance, administrative organization, and its role as a military and economic center during the 16th, 17th, and 18th centuries. It highlights the evolution of Karlovac from a military town to a free royal city in 1781, as well as its development as a trading center. The second section deals with the data from the death register. It begins with an analysis of the annual and monthly distribution of the deceased, revealing patterns or irregularities in mortality across different years and months. It also examines the age and gender structure of the deceased, with particular focus on infant and maternal mortality. To gain insight into the community's family dynamics, the social status and family structure of the deceased, such as singles, married individuals, and widows, are examined in detail. Additionally, the research investigates the origins of the deceased, with special attention given to various social groups, including the elite, military personnel, craftsmen, and postal workers. Lastly, the thesis explores the causes of death and places of death and burial. This master's thesis contributes to the study of the historical demography of Karlovac, providing insight into the structure of its population during the 18th century. The use of primary sources (parish death registers) and comparison with other similar areas places the demographic research of Karlovac within a broader context of studying pre-modern societies.