Introduction: No previous studies document the effects of both comprehensive tobacco control and its defunding on youth smoking. This study tests the effect of the youth-focused Minnesota Youth Tobacco Prevention Initiative (MYTPI) and its shutdown on youth smoking and determines whether these effects differed by age. Methods: The Minnesota Adolescent Community Cohort is a population-based, observational study designed to evaluate the MYTPI. The sample included cohorts of youth aged 12-16 years at baseline in Minnesota (N = 3,636) and a comparison group in six other Midwestern states (n = 605). Biannual surveys assessed youth smoking from October 2000, 5 months after the MYTPI launch, through October 2005, 2 years postshutdown. Adjusted piecewise linear trajectories predicted smoking stage (measured on a 1-6 continuum) comparing Minnesota with a comparison group during the MYTPI (Slope 1) and postshutdown (Slope 2) for each baseline age cohort. Analysis then compared baseline age cohorts with each other by centering their intercepts on age 16. Results: Neither slope of smoking stage differed between Minnesota and comparison groups, showing no period effects for the MYTPI or shutdown. However, younger cohorts, with early teen experience of MYTPI, smoked less than older cohorts by the same age. Mean smoking stage at age 16 differed by almost a half stage from the youngest (2.04) to the oldest (2.46) age cohort. Discussion: The study offers no evidence of period effects for the MYTPI or its shutdown. Design limitations, national or continued post-MYTPI statewide tobacco control efforts, or program flaws could explain the findings.