Social controls on sex and marriage, rooted in the political economy, regulated population in preindustrial Iceland. Married women had high fertility, offset by low illegitimacy and a means prerequisite for marriage. The number of married householders in their childbearing years responded to changes in population pressure, adjusting fertility and moving the population toward about 50,000, a level determined by both the sub‐Arctic environment and the political economy, which discouraged full use of available technology. [population regulation, population and agriculture, population and environment, population and political economy, preindustrial Iceland]