As of 1923 (interpreted from Form CT1000), the Pennsylvania Railroad was organized into Regions, Divisions, and Railroads. Railroads represented in bold are included in the listings but are believed to be independent railroads (many are confirmed so).
Central Region data courtesy of Robert Netzlof. (Anyone have the Western Region?)
| Region | Division | Railroad |
| Eastern Region | New Jersey Division | New York Division |
| Trenton Division | ||
| Camden Terminal Division | ||
| Atlantic Division | ||
| Hudson & Manhattan R.R. Co. | ||
| Philadelphia Terminal Division | ||
| Central Railroad of New Jersey | ||
| New York & Long Branch R.R. | ||
| Southern Division | Maryland Division | |
| Baltimore Division | ||
| Delaware Division | ||
| Norfolk Division | ||
| Baltimore, Chesapeake & Atlantic Ry. | ||
| Eastern Pennsylvania Division | Philadelphia Division | |
| Cumberland Valley Division | ||
| Middle Division | ||
| Tyrone Division | ||
| Cresson Division | ||
| Cresson Division, Cresson & Irvona Branch | ||
| Central Pennsylvania Division | Schuylkill Division | |
| Sunbury Division | ||
| Sunbury Division, Milroy Branch | ||
| Williamsport Division | ||
| Elmira Division | ||
| Elmira Division, Sodus Bay Branch | ||
| Central Region | Western Pennsylvania Division | Pittsburgh Division |
| Monogahela Division | ||
| Conemaugh Division | ||
| Monongahela Railway | ||
| Winfield Railroad | ||
| Northern Division | Renovo Division | |
| Buffalo Division | ||
| Buffalo Division Western New York and Pennsylvania Rwy |
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| Allegheny Division Western New York and Pennsylvania Rwy |
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| Eastern Ohio Division | Eastern Division | |
| Panhandle Division | ||
| Wheeling Division | ||
| Marietta Division | ||
| Lake Division | Cleveland & Pittsburgh Division | |
| Erie & Ashtabula Division | ||
| Akron Division | ||
