BACKGROUND: Adult smoking prevalence in Minnesota fell from 21.8% in 1997 to 15.2% in 2016. This reduction improved heart and lung health, prevented cancers, extended life and reduced healthcare costs, but quantifying these benefits is difficult. METHODS: 1.3 million individuals were simulated in a tobacco policy model to estimate the gains to Minnesotans from 1998 to 2017 in health, medical spending reductions and productivity gains due to reduced cigarette smoking. A constant prevalence scenario was created to simulate the tobacco harms that would have occurred had smoking prevalence stayed at 1997 levels. Those harms were compared with tobacco harms from a scenario of actual smoking prevalence in Minnesota from 1998 to 2017. RESULTS: The simulation model predicts that reducing cigarette smoking from 1998 to 2017 has prevented 4560 cancers, 31 691 hospitalisations for cardiovascular disease and diabetes, 12 881 respiratory disease hospitalisations and 4118 smoking-attributable deaths. Minnesotans spent an estimated $2.7 billion less in medical care and gained $2.4 billion in paid and unpaid productivity, inflation adjusted to 2017 US$. In sensitivity analysis, medical care savings ranged from $1.7 to $3.6 billion. CONCLUSIONS: Minnesota's investment in comprehensive tobacco control measures has driven down smoking rates, saved billions in medical care and productivity costs and prevented tobacco related diseases of its residents. The simulation method employed in this study can be adapted to other geographies and time periods to bring to light the invisible gains of tobacco control.