This research presents the correlation of undrained shear strength based on the cone resistance from the cone penetration test (CPT) for clayey soils in Indiana. It utilized the field cone penetration test program including the CPT, the index test, the one dimensional test and the triaxial test. The cone factor, which is essential to reliable estimation of undrained shear strength from cone resistance, has been evaluated considering the plasticity index of soils. The cone factor is influenced by the penetration rate during the CPT and test methods that are used for obtaining the undrained shear strength. The rate effect of the CPT has been examined to ensure undrained penetration, and the isotropic consolidated undrained compression test (CIUC) for shear strength assessment has been used to effectively reflect in-situ strength. Following the field cone penetration test program, clayey soils from 4 sites in Indiana have been investigated. Based on the results from the test program, the cone factor ranges from 8.0 at 7.9 I_p to 12.1 at 20.0 I_p for over-consolidated clays. This result parallels the increasing trend of the cone factor as the plasticity index increases, which was reported by Aas et al. (1986), while Lunne et al. (1976) and Baligh et al. (1980) showed decreasing trends. The equation N_k = 0.285 I_p +7.636  is suggested for estimating the cone factor in geotechnical design.