Historically, the scope of legalized gambling was limited in Ohio, but everything changed when a new constitutional amendment allowed four casinos to open. To better understand the impact of gambling expansion, a household survey was commissioned to determine the baseline estimate of problem gambling behaviours in the state before casinos opened. Participants were selected through multi-stage probability sampling, with over 3,500 respondents completing valid surveys. Nearly 60% of Ohioans gambled in the past year, but the statewide prevalence of problem gambling was relatively low; only 1.4% of persons scored high enough on the Problem Gambling Severity Index to be classified as a potential problem gambler (score ≥3). Regional estimates of problem gambling were highest for Franklin and Hamilton counties (both 5.0%) and lowest for Lucas and Cuyahoga counties (3.2% and 2.1%, respectively). Exploratory logistic regression modelling found that race, employment, education, family history of problem gambling, and feelings of depression increased the odds of being a problem gambler. Results will inform the discussion about current gambling problems and enable policy makers to design prevention strategies.