Quaternary ammonium compounds (QAC) are used in many commercial and household disinfection products. A method was developed to measure QAC occurrence in water discharged from three wastewater treatment plants during 2020 and 2021. Water samples (20 mL) were processed via solid phase extraction using weak cation exchange (WCX) cartridges (3 cc, 60 mg) and analyzed via liquid chromatography tandem mass spectrometry. Samples were analyzed for 12 QACs including benzethonium, six benzylalkyldimethyl ammonium compounds (BAC), three dialkyldimethyl ammonium compounds (DADMAC), and two ethylbenzylalkyldimethyl ammonium compounds (EBACs). QACs were detected in 100% of WWTP effluents with individual concentrations ranging 2.30-1,630 ng/L and total QAC concentrations (ΣQAC, the sum of 12 QAC) ranged 38.1-3,450 ng/L. The average concentrations of QACs detected in effluents was 49% BAC (average ΣBAC = 168 ng/L), 38% DADMAC (average ΣDADMAC = 119 ng/L), 9% EBACs (ΣEBAC = 25.0 ng/L), and 4% benzethonium (15.6 ng/L).