Objective: This study examines the association between political identity and young adults’ fertility desires from 1989-2019. Background: Political identity (defined as seeing oneself as preferring or aligned with either Republican or Democrats) is likely a predictor of fertility desires. Moreover, the increased salience of political identity suggests that the association between political identity and fertility desires has strengthened over time. Declining fertility rates and the increasing importance of political identity underscore the need to understand how political preferences inform desired family size. Method: Data come from the 1989–2019 waves of Monitoring the Future, a nationally representative study of 12th graders (N = 67,557). Regression models examined how political identity (measured by Republican or Democrat preference) predicts the desired number of children, measured both continuously and categorically. Results: Regardless of the period, Republicans desired more children than Democrats—a difference that grew over time, from 0.07 in 1989–1993 to 0.29 in 2014–2019. Differences in religiosity and attitudes toward gender and childbearing explained pre-2004 partisan gaps. In 2004 and later, much of the gaps were explained by religiosity and gender and childbearing attitudes, but Republicans still wanted more children than Democrats: relative to Democrats, Republicans had a higher probability of wanting four or more children in 2004–2013 and a lower probability of wanting to be childless in 2014–2019. Conclusion: Political identity has become increasingly salient for fertility desires, suggesting that identity might shape fertility preferences and future fertility behavior.