| Abbreviation | Definition |
|---|---|
| CIC | Cedar Rapids and Iowa City Railway |
| CIC | Cedar Rapids and Iowa City Railway (Crandic) |
| CIIU | Container-It |
| CIIX | Contico International |
| CIIX | Contico International Incorporated |
| CIM | Chicago and Illinois Midland Railway |
| CIND | Central Railroad Company of Indiana |
| CIND | Central Railroad of Indiana |
| CIPU | CAI International |
| CIPX | Central Illinois Public Service |
| CIPX | Central Illinois Public Service (Ameren Energy Generating) |
| CIR | City of Rochelle Illinois |
| CIR | City of Rochelle, Illinois |
| CIRR | Chattahoochee Industrial Railroad |
| CIRX | Consbec |
| CIRX | Consbec Incorporated |
| CIRY | Central Illinois Railroad |
| CISD | Colonel's Island Railroad |
| CISD | Colonel's Island Railroad Company |
| CISL | Cleveland, Indianapolis, and St. Louis Railway Company |