Biosolids and sludge are what remain after the liquid fraction of wastewater is separated during wastewater treatment. These high organic content matrices are known to contain organic contaminants, a few of which are the hazardous and environmentally persistent per- and polyfluoroalkyl substances (PFAS). The current study investigates whether sludge from a treatment facility serving mostly industrial establishments (moisture content: 98.6 %) and biosolids from a facility serving mostly domestic dwellings (moisture content: 72.1 %) retain these ‘forever chemicals’ similarly. Using 31 markers covering different PFAS classes, sludge was found to contain higher levels of a variety of PFAS (869 ± 791 ng/g; 21 of 31) than biosolids (31 ± 7 ng/g, 11 of 31). The most abundant PFAS was perfluorooctane sulfonic acid (PFOS), found mostly in sludge (range: 71–1300 ng/g versus 0–18 ng/g in biosolids). The large concentration variability in sludge was seasonal and sinusoidal. Sludge additionally contained all long chain PFAS, precursors (mostly surfactant ingredients and their transformation byproducts) and short chain PFAS (perhaps because of higher moisture content). By regression, sludge is also projected to contain twice as much PFAS as biosolids when the same amounts of samples are exposed to increasing PFAS concentration. Factors observed to cause differential PFAS retention between sludge and biosolids were moisture, chain length, input quality and functional group. Sulfonic acids for instance are one C atom shorter than carboxylates with similar occurrence in sludge and biosolids. More studies are needed to define the roles that factors not considered (e.g., organic carbon of sludge/biosolids, water chemistry and temperature) play in partitioning PFAS at treatment facilities. The existing Koc values for instance could not explain PFAS partitioning trends observed. Instead, the ratio of biosolids-to-influent concentrations was found to correlate positively with PFAS size. Using influent in the ratio, and not effluent, is novel. SynopsisSludge and biosolids are soil amendments; they contain hazardous and persistent PFAS. Methods of decoupling PFAS from these matrices start with understanding matrix-driven PFAS distribution as shown here.