The aggregation behaviour of three 1-alkyl-3-methylimidazolium chloride ionic liquids, [CnC1im]Cl (with n = 8, 10, 12), was probed at atmospheric pressure using density and speed of sound measurements in the 283.15 > T/K > 313.15 temperature range in aqueous solutions with mole fraction ranges of 0 > x([C8C1im]Cl) > 58×10-4, 0 > x([C10C1im]Cl) > 20×10-4, and 0 > x([C12C1im]Cl) > 4.8×10-4. The results were used to calculate partial molar volumetric data and the isentropic compressibility of the solutions, both of which can be used as relevant properties to probe aggregate formation. In this context, micelle formation, solvation phenomena and water structural changes within the solutions are discussed in terms of the temperature and concentration dependence of the calculated properties.