A circular plastic economy reduces raw material consumption and discourages pollution. Chemical recycling upgrades the quality of recyclate and is a complementary approach to thermomechanical recycling of plastic waste. This study investigated the use of aprotic and protic ionic liquids (ILs) as solvents for chemical recycling by hydrolysis of the most common polyester plastic, poly(ethylene terephthalate) (PET). Combinations of three types of cations (aprotic 1-alkyl-3-methylimidazolium, protic 1-methylimidazolium and protic 1,5-biazocyclo-[4.3.0]non-5-enium) combined with a range of anions (acetate, chloride, methanesulfonate, hydrogen sulfate, methyl sulfate, trifluoromethanesulfonate and chlorozincate) were used to hydrolyse PET in the presence of 15 wt% water as the co-solvent and reagent. PET conversion at the screening condition (180 °C, 3 h, 5% PET loading) varied between 1 – 100%, with ILs containing the acetate anion enabling >97% PET conversion irrespective of the cation. Acidification with aqueous HCl recovered crude crystallised terephthalic acid (TPA). Significant crude yields (46 – 93%) were only observed for the acetate ILs. The purity of the crude TPA varied between 34 – 98%, with 1-ethy-3-methylimidazolium acetate, [C₂C₁im][OAc], and 1-methylimidazolium acetate, [C₁Him][OAc], yielding purer TPA than 1,5-biazocyclo-[4.3.0]non-5-enium acetate, [DBNH][OAc]. It is also shown that PET conversion and TPA yield are correlated with high solubility of TPA at 5% solid loading. TPA solubility at 5% solid loading was correlated with the pK_a and the hydrogen bond acceptor strength of the IL anion. PET conversion and TPA yield generally correlated well with TPA solubility, suggesting that the depolymerisation mechanism in the acetate ILs is base catalysed. The screening identifies aqueous mixtures of the (pseudo) protic IL [C₁Him][OAc] as promising catalytic solvents for the chemical recycling of PET, as they generated high isolated TPA yields and good purities, whilst offering low ($1.74-2.15/kg) solvent cost of PET at an industrially feasible temperature. However, an effective separation approach for the monomers TPA and ethylene glycol from the solvent remains to be developed.