<p>The aging of Mexican-born undocumented farmworkers in the U.S. may compromise agricultural productivity and lead to increasing chronic disease in this population, yet research on aging and chronic disease among undocumented U.S. farmworkers is scarce. Observations were drawn from the National Agricultural Workers Survey (2001–2018). Our primary analyses focused on Mexican-born undocumented farmworkers aged 18 and older (<i>n</i> = 17,606). As a comparison, we descriptively examined Mexican-born farmworkers who were legal permanent residents (<i>n</i> = 8,216) or U.S. citizens (<i>n</i> = 1,608). Among undocumented farmworkers, we examined population aging from 2001 to 2018 and tested whether number of chronic conditions (self-reported doctor-diagnosed diabetes, hypertension, heart disease, and asthma), multimorbidity (≥ 2 chronic conditions), and individual conditions varied by age group and time. Statistical methods included weighted linear, negative binomial, and logistic regression. Undocumented Mexican-born farmworkers appeared to have the greatest increase in mean age but were consistently younger than the other legal status groups. Based on adjusted inferential analyses, the mean age of Mexican-born undocumented farmworkers increased by 9.4 years (95% CI:8.8–10.0) from 2001– 2002 to 2017–2018. Number of chronic conditions and the likelihood of multimorbidity or diabetes was greater among older undocumented farmworkers compared with other legal status groups. There was some evidence that chronic disease burden was greater in later waves. This study documents aging and potential growth in chronic disease burden among Mexican-born undocumented U.S. farmworkers. Our findings highlight the need for practical immigration policies, workplace protections, and chronic disease prevention tailored to undocumented U.S. farmworkers.</p>