Justin (Yaotian) Zhang

Most studies of cannabis legalization focus only on the legalizing state, yet the enforcement burden can cross into neighbors that still prohibit it. Illinois opened a legal cannabis market in January 2020 while neighboring Iowa kept prohibition. Using a county–year difference-in-differences design with NIBRS offense counts (2015–2022), I compare the seven Iowa counties connected to Illinois by a direct highway bridge against the ninety-two interior counties. The event study does not reject parallel pre-trends. Recorded drug offenses in bridge counties rose by about 26% relative to the interior (β = 0.233, p = 0.024) and—more consequentially—recorded property offenses climbed about 37% (β = 0.312, p = 0.005), reaching a category that legalization does not directly cause. Violent offenses are positive but noisy, and driving offenses are flat. A cost–benefit account that counts only in-state tax revenue therefore understates the burden legalization places on its neighbor.