Incineration is commonly used to dispose of waste contaminated with per- and polyfluoroalkyl substances (PFAS), despite few experimental data supporting the efficacy of this technique. To investigate the prevalence of PFAS in residuals from Swedish municipal waste incineration (MWI) plants, samples of fly ash, bottom ash, and flue gas condensate were collected from 27 of Sweden’s 38 plants and analyzed for 13 perfluoroalkyl acids (PFAAs). ∑₁₃PFAA concentrations ranged from 0.28 to 180 ng/L, 0.22–1.6 μg/kg, and 0.18–38 μg/kg, in condensate, bottom ash, and fly ash, respectively (detection frequencies of 79, 21, and 30%, respectively). Total fluorine (TF) measurements in a subset of samples revealed concentrations of <0.20–11 mg F/L in condensate (n = 8) and 120–5400 μg F/g in ashes (n = 8), the former of which was primarily attributed to inorganic fluorine. Extractable organofluorine (EOF) exceeded ∑₁₃PFAA concentrations by up to 3 orders of magnitude (0.70–16 μg F/g in fly ash [n = 3] and <0.80–9.0 μg F/L for condensate [n = 2]), suggesting that the majority of fluorine occurring in MWI residuals remains unidentified. Collectively, these data demonstrate that despite temperatures exceeding 1000 °C, PFAAs and other fluorinated substances may form and/or persist during incineration and risk being released to the environment via MWI residues.