Objective This study examines the association between political identity and young adults' fertility desires from 1989 to 2019. Background Understanding the factors that shape fertility preferences is important because these preferences are the critical bridge between social forces and fertility. Identity is a theorized, but understudied, predictor of fertility desires. The increasing salience of political identity suggests that the association between political identity and fertility desires has strengthened over time. 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. From 2004 and onward, these factors attenuated, but did not fully explain, Republican–Democrat gaps. In later periods, relative to Democrats, Republicans still wanted more children on average, had a higher probability of wanting four or more children in 2004–2013 and a lower probability of eschewing parenthood in 2014–2019. Conclusion Political identity has become increasingly salient for fertility desires, suggesting that identity might shape fertility intentions and future fertility behavior.