Thanks to a reader for pointing this out to us. The New York Times published a story and an interactive map to show the lines of demarcation between baseball fans of nearby cities. For example, at what point between Boston and New York do people become fans of the Red Sox vs. the Yankees.
One feature of the map allows you to search by zip code and see what teams the locals root for. We searched 19428 and found that 81% of the residents in the zip code are fans of the Philadelphia Phillies. Six percent of the zip code is devoted to the New York Yankees and 3% are fans of the Boston Red Sox. The map only provides details on the top three fan bases, so there is 10% of the population unaccounted for.
Check it out.