Over the next 10 years, Metrolinx will be developing a Regional Express Railway (RER) system by retrofitting existing GO transit lines. The RER project is one of several components of the Government of Ontario's Moving Forward Plan announced in 2015, aiming to increase transit ridership and accessibility through frequent all-day service, electrified routes, and faster travel times (Metrolinx, 2015a). RER development requires careful planning to determine where additional infrastructure can be physically placed, while simultaneously providing access to the demographics most in need of it. In this study, census tracts within the Golden Horseshoe already served by existing GO rail service are analyzed to identify the optimal areas to develop new RER stations. The criteria include a number of socio-economic factors such as population density, income, immigration status, and age, constrained by the technical limitations of railway retrofication.