Objective To assess the association of reported smoking cessation at various time points during pregnancy with fetal growth restriction (FGR). Methods This was a population-based retrospective cohort study of singleton nonanomalous live births using Ohio birth certificates, 2006–2012. Outcomes of women who reported smoking only in the 3 months before conception and women who reported smoking through the first, second, or third trimester were compared to a referent group of nonsmokers. Multivariate logistic regression assessed the association between smoking cessation at various times in pregnancy and FGR less than the 10th and 5th percentiles. Results Of 927,424 births analyzed, 75% did not smoke. Of smokers, 24% smoked preconception only, 10% quit after the 1st trimester, 4% quit after the 2nd trimester, and 59% smoked throughout pregnancy. The rate of FGR less than the 10th and 5th percentiles among non-smokers was 8.1% and 3.6%, respectively. Although smoking only in the preconception period did not significantly increase FGR risk, smoking in any trimester did. The adjOR(95%CI) for FGR less than the 10th and 5th percentiles, respectively, of cessation after the 1st trimester was 1.19(1.13,1.24) and 1.25(1.17,1.33), and 1.67(1.57,1.78) and 1.83(1.68,1.99) for cessation after the second trimester. Women who reported smoking throughout pregnancy had the highest risks of FGR, 2.26 (2.22,2.31) and 2.44(2.37,2.51), after accounting for the influence of race, low socioeconomic status, and medical comorbidities. Conclusions Smoking of any duration during pregnancy is associated with an increased risk of FGR, with decreasing risk the earlier that cessation occurs. Smoking cessation programs should focus on the benefit of quitting as early in pregnancy as possible.