Most quantitative research on segregation and neighborhood change in American cities prior to 1940 has utilized data published by the Census Bureau at the ward level. The transcription of census manuscripts has made it possible to aggregate individual records to a finer level, the enumeration district (ED). Advances in Geographic Information Systems (GIS) have facilitated mapping these data, opening new possibilities for historical GIS research. We report here the creation of a mapped public use data set for EDs in ten northern cities for each decade from 1900 to 1930. We illustrate a range of research topics that can now be pursued: recruitment into ethnic neighborhoods, the effects of comprehensive zoning on neighborhood change, and white flight from black neighbors.