Pennsbury is a unique borough in that it is entirely a municipality of condo-style houses, having been built in 1973. In 1976, there was a disagreement with Robinson Township over proposed sewage treatment fees, which triggered the self-government attempt. In 1977, it separated from the surrounding township and became an Allegheny County borough. The words of the Declaration of Secession included "that we can govern our affairs more effectively and equitable than a distant and disinterested authority". The first council of officials and a mayor were elected and took office in January, 1977.
The population was 677 at the 2020 census.