Research in the obscure domicile files of Poznań’s Municipal Records reveals that in late nineteenth- and early twentieth-century Poznań, fertility was determined by the interaction of many socioeconomic factors. Mothers’ birth cohort and husbands’ socioeconomic status proved to be the strongest factors significantly influencing women’s age at matrimony, their age at first birth, and their number of children. Women born before 1890 married and started giving birth to the first child later than those born after 1890. The wives of workers and craftsmen started reproduction earlier and had more children than those of white-collar professionals. Religion did not influence women’s age at marriage and age at first birth, but it did influence their number of children.