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
Allegheny Division
Western New York and Pennsylvania Rwy
Eastern Ohio Division Eastern Division
Panhandle Division
Wheeling Division
Marietta Division
Lake Division Cleveland & Pittsburgh Division
Erie & Ashtabula Division
Akron Division