The study of segregation is essential for understanding how place influences life outcomes. Traditional segregation indices rely heavily on the use of areal units for calculation, which risks introducing both measurement and interpretation error. Using individual-level data avoids many of the problems facing traditional area-level indices. However, few segregation indices currently exist that are capable of utilizing such data. Given that our understanding is only as good as our measurement, it is imperative that our measures accurately reflect our perceptions of segregation. Utilizing the recent release of the complete 1940 Census count data, this article details a new individual-level segregation measure--the shortest path isolation (SPI) index. The SPI index captures the degree of racial isolation experienced by an individual, regarding both distance and interpersonal contact. With West Philadelphia as a sample study area, this article highlights the benefits of the SPI index for studying segregation at the individual level.