Illite-based geopolymer products through activating of three Quaternary clays of Latvia by different concentration of KOH solution was investigated. Potassium hydroxide concentration in the aqueous phase of the geopolymeric system acted on the dissolution process, as well as on the bonding of the solid particles in the final structure. Depending on the different SiO2/Al2O3 ratio in the used clays (2,7 for clay K1, 3,5 for clay K2 and 3,8 for clay K3) decreased mechanical strength of the obtained samples. The best mechanical strength (30 MPa) showed clay K1 with the smallest SiO2/Al2O3 ratio. Scanning electron microscopy and mercury porosimetry results confirmed the differences among activated clays developing the diverse mechanical strength of the obtained samples.