Objective Policies raising the minimum legal sales age (MLSA) of tobacco products to 21 are commonly referred to as tobacco 21. This study sought to identify components of tobacco 21 policies and develop an instrument to examine policy language within 16 state laws adopted by July 2019. Methods The multistage tool development process began with a review of established literature and existing tobacco 21 policies. In a series of meetings, tobacco control experts identified key policy components used to develop an initial tool. After testing and revisions, the instrument was used to code the existing tobacco 21 state-level policies. Inter-rater reliability (κ=0.70) was measured and discrepancies were discussed until consensus was met. Policy component frequencies were reported by state. Results While all 16 states raised the MLSA to 21, the laws varied widely. Two laws omitted purchaser identification requirements. Fifteen laws mentioned enforcement would include inspections, but only three provided justification for conducting inspections. All 16 states provided a penalty structure for retailer/clerk violations, but penalties ranged considerably. Fourteen states required a tobacco retail licence, nine renewed annually. Six laws contained a military exemption, five were phased-in and 10 contained purchase, use or possession laws, which penalised youth. Four states introduced or expanded pre-emption of local tobacco control. Conclusions The instrument developed is the first to examine policy components within state-level tobacco 21 laws. Policies that include negative components or omit positive components may not effectively prevent retailers from selling to youth, which could result in less effective laws.