Experimental solubilities of acetaminophen and ibuprofen in polyethylene glycol 600–water, ethanol–polyethylene glycol 600, and polyethylene glycol 600–water–ethanol mixtures at 25 °C are reported. The solubilities of drugs in the presence of ethanol and polyethylene glycol 600 were increased. The Jouyban–Acree model was used to fit the solubility data of each drug in the binary mixtures in which the overall mean relative deviations (OMRDs) for acetaminophen and ibuprofen were 2.9% and 4.3%, respectively. The OMRDs for ternary solvent mixtures for acetaminophen and ibuprofen were 16.8% and 22.4%, respectively. Generally, the errors associated with ibuprofen are larger than that of acetaminophen in both binary and ternary solvent mixtures. The solubilities were predicted using previously trained versions of the Jouyban–Acree and log-linear models with the OMRDs of 38.8% and 52.1%, respectively. Density of the mixed solvents in the absence of the solute was measured and used to train the model and then the density of the saturated solutions was predicted using the trained model and the density of the saturated solutions in mono-solvent systems with the OMRD of 3.2%.