Regionally, soils with illitic mineralogy are important because they are concentrated in the Midwest. Increased rural development in northeastern Indiana prompted a detailed investigation of the physical, chemical, and mineralogical properties of the illitic soils in this region. A northeast – southwest transect across the Bluffton till plain and associated moraines was established in northeastern Indiana. Twelve Aeric Epiaqualfs and Aquic Hapludalfs were sampled on backslope and shoulder landscape positions on the till plain and summit positions on the moraines. Clay percentages across the transect ranged from 36 to 52% in the Bt horizon and 24 to 36% in the Cd horizon. The fine and coarse clay fractions contained illite, vermiculite, hydroxy-interlayered vermiculite and kaolinite; these were identified using x-ray diffraction and alkylammonium methods. Additional mineral characterization with alkylammonium methods and high-resolution transmission electron microscopy will be discussed.