National Archives and Records Administration (NARA)

As another federal administration that maintains historic records, NARA also holds a collection of government made maps which feature railroads. 

• Railroad Maps in the Cartographic Research Room at NARA External 
   

State libraries and archives

For railroad maps of more local areas considering looking into the collections held at state libraries and archives.
 

Academic archives

Similarly, academic institutions may hold railroad related material as it pertains to their location and the history of the area.
 

Historical societies

Counties and towns sometimes collect and archival historic material related to the area. Occasionally societies are also created around particular subjects matter rather than a location. For example, the Baltimore and Ohio Railroad Historical Society aptly maintains material on the Baltimore and Ohio Railroad.

• Baltimore and Ohio Railroad Historical Society External 

For more modern railroad maps it can be worth consulting the websites of other government agencies and institutions.
 

United States Department of Transportation

• Federal Railroad Administration (FRA) External - A branch of the US Department of Transportation, the FRA is the authoritative source on railroad information and data in the United States. It produces railroad related maps using geographic information system data.
• State branches of the Department of Transportation (DOT)- Many state branches of the DOT offer contemporary railroad maps of their jurisdiction along with related data and statistics.
   

Surface Transportation Board

• National Rail Network Map External- This map was compiled by staff at the STB based on the National Transportation Atlas Dataset, maintained by the Bureau of Transportation Statistics within the U.S. Department of Transportation.
   

Smithsonian Institution

• Maps Research Guide External -This guide compiled by the Smithsonian institution includes links for searching the Smithsonian's own map collections and also lists a variety of other prominent map collections around the globe and online.