Background Public libraries may promote health through literacy, education and social connections. Objective To conduct the first broad‐based, quantitative exploration of health and public library patronage. Methods Retrospective cross‐sectional study. All 2925 adult patients at a general practice clinic living in a small north‐eastern U.S. city were invited by mail to participate; 243 consented. Clinical variables from the medical records were combined with library usage variables from the public library patron database. The authors analysed how patient health characteristics were associated with library cardholding, average card use or recency of use. Results Approximately 72% of participants held a library card; 40% of these had used it within the last month. Library cardholding was not associated with patient characteristics. Higher average card use was associated with pregnancy, having youth at home and depression severity. Lack of recent library usage was associated with current smoking (P = 0.01) and drug use (P = 0.01). Among ever‐smokers, moderate/high card use and card use within six months were both associated with over two times the odds of quitting smoking. Conclusions Public libraries and health appear to intersect around substance abuse and depression–anxiety disorders. Moderate or higher use of public libraries is strongly associated with tobacco cessation.