Phytophthora sojae, the causal agent of Phytophthora root and stem rot (PRR) of soybean, is an oomycete pathogen that can cause significant soybean yield reductions. A 2014 study estimated that annual yield losses attributed to PRR across the North Central region of the United States were 33 million bushels. This disease can be managed effectively through R-gene mediated resistance, but previous studies have shown an increasing number of P. sojae isolates that can adapt to the resistance conferred by several commonly deployed Rps (Resistance to Phytophthora sojae) genes. This study examined the population pathotype diversity among P. sojae isolates collected from Ohio, Indiana, and Kentucky to evaluate the effectiveness of a set of R genes. Each isolate of P. sojae was tested on a set of 16 differential lines containing the following Rps genes: Rps1a, Rps1b, Rps1c, Rps1d, Rps1k, Rps2, Rps3a, Rps3b, Rps3c, Rps4, Rps5, Rps6, Rps7 and Rps8. Preliminary results show an average pathotype complexity of 6.74 on 15 differential lines based on 416 isolates from Ohio, Indiana, and Kentucky. Specifically, 206 P. sojae isolates from Ohio had an average pathotype complexity of 8.02, while 122 isolates from Indiana and 88 isolates from Kentucky had average pathotype complexities of 5.67and 5.22, respectively. The results of this study provide valuable and current information to soybean breeders and farmers about the effectiveness of different Rps genes across these three states, as well as showing the importance of combining multiple types of resistance to manage this disease.