Abstract The aim of the article is to determine how depopulation, low fertility, population ageing, and migration processes affect Poland’s security in a comparative perspective of the Visegrad Group (V4) countries: the Czech Republic, Poland, Slovakia, and Hungary. The study is presented within the framework of the theory of the second demographic transition and the sectoral approach to security. It is assumed that demographic transformations are not solely a matter of social policy but constitute a long term factor shaping the state’s potential in the social, economic, industrial, military, and cultural dimensions. A comparative analysis was conducted using demographic and forecast data from Eurostat, the Statistics Poland (GUS), as well as strategic documents and family policy programmes of the V4 countries. The findings indicate that all Visegrad Group states experience persistently low fertility, below the level of simple generational replacement, along with a growing share of older persons and a shrinking pool of working age population. The study demonstrates that financial transfers to families may reduce material barriers to parenthood but, on their own, do not lead to a sustained increase in fertility. More effective outcomes are achieved through coherent policies encompassing accessible housing, childcare provision, employment stability, equal labour market opportunities for women and men, reproductive health services, migrant integration policies, and the activation of older persons (P. McDonald, 2006, pp. 501–506).