Occurrence and fate of six neonicotinoids (imidacloprid, clothianidin, acetamiprid, thiamethoxam, thiacloprid, and dinotefuran) and one degradate (acetamiprid-N-desmethyl) were studied in a United States municipal wastewater treatment plant (WWTP) and an engineered wetland downstream. Flow-weighted samples collected in a five-day monitoring campaign were analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS) using methods of isotope dilution and standard addition. Three of the six neonicotinoids were detected. Daily loads of imidacloprid and acetamiprid were stable, whereas those of clothianidin varied. Detected 5-day average concentrations in WWTP influent and effluent were 54.7 ± 9.3 and 48.6 ± 8.4 ng/L for imidacloprid, 3.7 ± 0.8 and 1.7 ± 0.5 ng/L for acetamiprid, and 149.7 ± 273.1 and 116.7 ± 144.9 ng/L for clothianidin, respectively. Concentrations of neonicotinoids in digested sludge were below the limit of detection (<2 μg/kg dry weight). Wetland monitoring revealed lack of removal for imidacloprid and acetamiprid. Hazard quotient (HQ) analysis showed values of larger than unity for imidacloprid (1.4 ± 0.1) and total neonicotinoids (4.8 ± 4.5) in WWTP effluent. Thus, imidacloprid, acetamiprid, and clothianidin were shown to occur in United States wastewater, persist during conventional and wetland treatment, and to pose potential risk in effluent-dominated, receiving surface waters.