The decline in fertility occurring throughout the first half of the 20th century in the United States and preceding the baby boom remains largely unexplored. This paper presents empirical and theoretical evidence linking this decline to the spread of electricity. Using data on early electrification efforts, I empirically disentangle the two channels linking electrification and fertility: the introduction of time-saving appliances that reduce the time needed for child-rearing; and the rise in female wages which raises the opportunity cost of childcare. I then use these empirical estimates to calibrate a model that features both channels and quantifies the aggregate impact of electrification on fertility. I find that electrification explains 4.6% of the overall fertility decline in 1900-1940 in the US, and that the opportunity cost channel is preponderant in explaining this response by allowing young childless women to benefit from the labor market gains of electricity.