| 1 | CIR | Arctic Circle Air Service, Inc. | IATA: 5F, Callsign: Air Arctic, | USA | AVCODES |
| 2 | CIR | Arctic Circle Air Service | IATA: 5F | | ICAO1 |
| 3 | CIR | City of Rochelle, Illinois | 7/2000-7/2005 | | NAKINA |
| 4 | CIR | City of Rochelle, Illinois | Jul-00 | | NRHS |
| 5 | CIR | *CENTRAL IOWA RAILROAD | | | PWRC |
| 6 | CIR | +CITY OF ROCHELLE, ILLINOIS | | | PWRC |
| 7 | CIR | City of Rochelle, Illinois | | | RSRV |
| 8 | CIR | CITY OF ROCHELLE ILLINOIS | | | SCAC4 |
| 9 | CIRB | CIRCLE B CARRIERS | | | SCAC4 |
| 10 | CIRC | Central Iowa Transportation Cooperative d/b/a Central Iowa Ry. Co. | 1/1975; eliminated 7/1976; 1/1980 | | NAKINA |
| 11 | CIRC | Central Iowa Ry. Co. | added 4/1974 | | NAKINA |
| 12 | CIRC | Central Iowa Ry. Co. | added 4/74 | | NRHS |
| 13 | CIRC | Central Iowa Transportation Cooperative d/b/a Central Iowa Ry. Co. | 1/75; eliminated 7/76; 1/80 | | NRHS |
| 14 | CIRC | *CENTRAL IOWA RAILWAY CO. | | | PWRC |
| 15 | CIRC | *CONSOLIDATED INSPECTION & REPAIR CORP. | | | PWRC |
| 16 | CIRD | CHICAGO INTERMODAL TRANSPORTATION I | | | SCAC3 |
| 17 | CIRD | CHICAGO INTERMODAL TRANSPORTATION I | | | SCAC4 |
| 18 | CIRF | CIRCLE FOUR TRANSFER INC | | | SCAC3 |
| 19 | CIRG | CAL INLAND REFRIGERATED SERVICES IN | | | SCAC3 |
| 20 | CIRH | CSI INTERNATIONAL INC | | | SCAC4 |
| 21 | CIRI | CIRI - COLLINS LOGISTICS LLC | | | SCAC4 |
| 22 | CIRJ | CIRCLE P | | | SCAC4 |
| 23 | CIRM | CIRCLE M CARTAGE INC | | | SCAC3 |
| 24 | CIRN | CIRCLE A CONSTRUCTION INC | | | SCAC3 |
| 25 | CIRO | CAMDEN IRON & METAL INC/BANTIUOGLIO | | | SCAC3 |
| 26 | CIRO | CAMDEN IRON & METAL INC | | | SCAC4 |
| 27 | CIRP | CIRCLE P TRUCKING INC | | | SCAC3 |
| 28 | CIRP | CIRCLE S TRANSPORTATION OF ARKANSAS | | | SCAC4 |
| 29 | CIRQ | CIRCLE AIRFREIGHT CORP | | | SCAC3 |
| 30 | CIRQ | CIRCLE AIRFREIGHT CORP | | | SCAC4 |
| 31 | CIRR | Chattahoochee Industrial R.R. | 1/1975-7/2005 | | NAKINA |
| 32 | CIRR | Chattahoochee Industrial R.R. | 1/75-7/2000 | | NRHS |
| 33 | CIRR | CHATTAHOOCHEE INDUSTRIAL RAILROAD | | | PWRC |
| 34 | CIRR | Chattahoochee Industrial Railroad | | | RSRV |
| 35 | CIRR | CHATTAHOOCHEE INDUSTRIAL RAILROAD | | | SCAC3 |
| 36 | CIRR | Chattahoochee Industrial Railroad | | USA | TRAFFIC |
| 37 | CIRS | CIRCLE S TRANSPORT INC | | | SCAC4 |
| 38 | CIRT | CAIRO SALT COMPANY INC | | | SCAC3 |
| 39 | CIRU | CAROTRANS INTERNATIONAL | | | SCAC3 |
| 40 | CIRU | COMMISSIONARIA INTERTRASPORTI SRL | | | SCAC4 |
| 41 | CIRV | CIRCLE VAN & STORAGE INC | | | SCAC4 |
| 42 | CIRX | Consbec Inc. | added 4/1997; 7/2000; eliminated 10/2001; 7/2005 (not listed) | | NAKINA |
| 43 | CIRX | Consbec Inc. | added 4/97; 7/2000 | | NRHS |
| 44 | CIRX | *CITY ISLAND RAILROAD, INC. | | | PWRC |
| 45 | CIRX | +CONSBEC INCORPORATED | | | PWRC |
| 46 | CIRX | Consbec | | | RSRV |
| 47 | CIRY | Central Illinois R.R. Co. | 7/2005 | | NAKINA |
| 48 | CIRY | CENTRAL ILLINOIS RAILROAD CO. | | | PWRC |
| 49 | CIRY | Central Illinois Railroad | | | RSRV |
| 50 | CIRY | CENTRAL ILLINOIS RAILROAD COMPANY | | | SCAC4 |