Forced population movement and its consequences on recipient countries is a major concern in nations around the world. Finland provides a unique opportunity to understand the long term effects on family formation patterns of involuntary migration in low fertility contexts. Using register data that cover the years 1988-2011, we study people who were forced to migrate from Karelia as children in the 1940s, and compare their reproductive and partnering patterns with socioeconomically similar people who were not forced to migrate. These underpinnings come close to a quasi-natural experiment in that all individuals had to leave the ceded area, none were selected on characteristics that affect fertility, and none had the opportunity to eventually return migrate. We find that displaced persons were notably more likely than their non-displaced counterparts to have a partner who also was born in Ceded Karelia. Even though the overall association between forced migration and reproductive patterns are modest, this assortative mating behaviour tends to affect fertility in a positive manner. Being born in Ceded Karelia does not only make people more likely to have a partner born in Ceded Karelia, but this combination appears to increase the likelihood of having children. The interrelation between migration and fertility is consequently dependent on partner characteristics.