Aim. The article provides an analysis of Polish national censuses data in order to track changes that families and households in Poland have undergone over the past few decades and in order to answer the question whether these changes are in compliance with the assertions of the second demographic transition theory. Methods and materials. Moreover, the article uses data of the National Statistical Office on marriages, divorces, births and deaths, since the processes of marital formation and dissolution, as well as fertility and other demographic trends, impact directly on the number and structure of families and households. Emphasis is on the decade between the last two censuses of 2011 and 2021. Analysis is supplemented by conclusions from relevant research on the same topic. Results and conclusion. In the first place, changes affecting families and households in Poland are strongly influenced by the aging of the country’s population. As a result, the number of both households and families is declining. Also, some of the tenets of the second demographic transition theory are evidenced in the changes of the structure thereof: reduced average number of household members, reduced number of children in families and dynamic increase in the number of informal unions. These phenomena refer in particular to the inhabitants of urban areas.