To examine the correct application of the $0.01/ounce Cook County, Illinois, Sweetened Beverage Tax on sugar-sweetened and artificially sweetened beverages, a total of 111 beverage products were purchased from 28 food stores in September and November 2017. Purchases were categorized by taxable (sugar-sweetened and artificially sweetened soda and juice drinks) and nontaxable (100% fruit juice and sparkling water) beverage type, store type (limited service vs supermarket/grocery), and area median household income (lower vs higher). Two-sample tests of proportions were conducted to compare correctly taxed purchases. The tax was correctly applied in 91.0% of cases. Correct tax application was found in 87.8% of taxable beverage purchases versus 97.3% of nontaxable beverage purchases (P = .10), 71.4% of juice drink purchases versus 95.6% of nonjuice drink purchases (P < .001), and 85.5% of limited service store purchases versus 100% of supermarket/grocery purchases (P = .01). No significant differences were found by area income.