| J and J Leasing | MGMX | added 4/89; eliminated 10/89 | |
| J and J Partnership | MGMX | added 10/89; eliminated 10/93; 1/94-7/2000 | |
| J and J R.R., Inc. | JJRD | added 4/86; eliminated 1/91; 1/94-7/2000 | |
| J. Dietrich & Co. | JDAX | Apr-38 | |
| J. Neils Lumber Co. | JNLX | 4/38 & 10/57; eliminated 10/58 | |
| J.A. Garfield | JAGX | 10/57-10/66; eliminated 7/67 | |
| J.A. LaFortune | JAFX | Apr-38 | |
| J.E. Thompson and Associates | JETX | 10/57-4/61 | |
| J.H. Leftwich & Co., Inc. | JHLX | 7/65-10/66; eliminated 10/68 | |
| J.K. Line, Inc. | JKL | 1/94-7/2000 | |
| J.M. Fox | FOX | 10/57; eliminated 1/59 | |
| J.M. Huber Corp. | JMHX | 4/38-7/2000 | |
| J.M. Huber Inc. | HLCX | Apr-38 | |
| J.R. Lawrence | JRLX | 1/52-4/61 | |
| J.R. Simplot Co. | JRSX | added 10/60; 4/61-4/70; eliminated 1/74; added 10/87; 1/94-7/2000 | |
| J.S. Young Co. | JSYX | 1/52-4/70; eliminated 4/73 | |
| J.T. Baker Chemical Co., Taylor Chemical Division | JTBX | 1/52-10/66; eliminated 4/69 | |
| J.W. Flammer Co., Inc. | JWFX | added 4/68; 4/70-1/80; eliminated 4/89 | |
| J.W. Kerslake Co. | JWKX | added 1/71; 1/75-1/80 | |
| Jack F. Duckworth | JFDX | added 1/72; 1/75; eliminated 4/75 | |
| Jackson and Southern R.R. Co. | JSRC | added 10/84; eliminated 1/95; eliminated 7/95; 7/2000 | |
| Jacksonville Electric Authority | SJRX | added 10/86; 1/94; eliminated 1/95; 7/2000 | |
| Jacksonville Terminal Co. | JTCO | 1/75-7/2000 | |
| Jacob Dold Packing Co. (Refrigerator Cars) | JDPX | Apr-38 | |
| Jacob Stern & Sons, Inc. | JSX | 4/38-1/75; eliminated 4/76 | |
| Jaffe Car Lines, Inc. | JCLX | eliminated 7/79 | |
| Jahncke Service, Inc. | JSIX | added 1/65; 7/65-4/70; eliminated 1/74 | |
| JAIX Leasing Co. | JAIX | added 1/96; 7/2000 | |
| JALX | added 10/96; 7/2000 | ||
| James B. Berry Sons' Co., Inc. | JBBX | Apr-38 | |
| James B. Clow & Sons | JBCX | 4/38-1/52 | |
| James B. Shatto Co., Inc. | JBSX | added 1/58; eliminated 7/58 | |
| James C. McCanless | JCMX | added 4/78; 1/80; eliminated 4/88 | |
| James Griffiths & Sons | JGS | 1/75-1/80 | |
| James Quinlan, Inc. | JQGX | 7/65-1/80; eliminated 7/82 | |
| Jan, Inc. | JANX | added 4/89; eliminated 7/92; 1/94-7/2000 | |
| Jansen Rail Car, Inc. | JRCX | added 7/90; 1/94; eliminated 7/96 | |
| COTX | added 4/89; 1/94; eliminated 1/96 | ||
| KDEX | added 4/89; 1/94; eliminated 1/96 | ||
| Jaxport Terminal Ry. Co. | JXPT | added 1/90; 1/94; eliminated 10/97 | |
| Jay B.S. Corp. | JBSX | added 7/58; eliminated 10/59 | |
| Jefferson Warrior R.R. Co., Inc. | JEFW | 1/94-7/2000 | |
| Jeffersonville Silgas, Inc. | SILX | 1/52-10/66; eliminated 10/69 | |
| Jeffrey J. Kelling | IFOX | added 1/87; eliminated 7/89 | |
| Jennison-Wright Corp. | JWX | 4/38-1/75 | |
| Jersey Shore Steel Co. | JSSX | Jul-00 | |
| Jerseyville & Eastern R.R. | JE | 4/61-7/65 & 1/75-1/80 | |
| Jewett & Sherman Co. | JSMX | 4/38-7/65; eliminated 1/66 | |
| Jim Dobbes, Inc. | JDIX | Jul-00 | |
| Jim Walter Resources Inc. (captive service) | JWRX | Jan-94 | |
| Jimbetco, Inc. | JBIX | added 1/80; 1/80; eliminated 1/81 | |
| JJ Rail Car Leasing Ltd. | JJJX | added 1/95; 7/2000 | |
| JNS Marketing Co., Coastline Rail Service Division | JNSX | Jul-00 | |
| John A. Roebling's Sons Co. | JARX | 4/38-1/52 | |
| John A. Roebling's Sons Corp., subsidiary of the Colorado Fuel and Iron Corp. | JARX | 10/57; eliminated 7/58 | |
| John E. Shatford, Agent | CMTX | Apr-38 | |
| John F. Stegner Co. (National Car Co.) | JFSX | Apr-38 | |
| John H. Grace Co. | CANX | added 10/53; eliminated 4/54 | |
| GRYX | 4/38-7/2000 | ||
| PTLX | eliminated 4/57 | ||
| John H. Witte & Sons | JHWX | Apr-38 | |
| John Kenneth Burbridge | JKBX | Jul-00 | |
| John Neas Tank Lines | JNTX | added 4/80; eliminated 4/87 | |
| John Neas Tank Lines, Inc. | JNTX | added 4/87; eliminated 7/91 | |
| John Powell Chemical Co. | JPCX | Jan-52 | |
| John S. Carlson and Co., Inc. | JCEX | added 4/81; eliminated 1/86 | |
| John W. Chartrand (Chartrand's Traffic Service) | CHAX | Jan-52 | |
| John. L. McCarthy | JLMX | eliminated 1/90 | |
| Johnson Oil Refining Co. | JORX | 4/38-1/52; eliminated 7/56 | |
| Johnsonburg, Kane, Warren & Irvine R.R. Co. | JKWI | added 10/82 | |
| Johnstown & Stony Creek R.R. | J&SC | Apr-38 | |
| Johnstown America Corp. | JACX | added 7/92; 1/94-7/2000 | |
| Johnstown and Stony Creek R.R. Co. | JSC | 1/75-1/80; eliminated 10/83 | |
| Jones & Laughlin Steel Corp. | JLSX | 4/38-10/66; eliminated 1/70 | |
| Jones Chemicals, Inc. | JCIX | 7/65-1/80; eliminated 7/84 | |
| Joplin-Pittsburg R.R. | J&P | Apr-38 | |
| Joppa & Eastern R.R. Co. | JE | 1/94; added 10/96; eliminated 7/99; 7/2000; added 7/2001 | |
| Jordan Co. | JCOX | 1/52-4/70; eliminated 4/71 | |
| Jormac, S.A. de C.V. | JORX | added 1/95; 7/2000 | |
| Jos. A. Likely, Ltd. | JALX | 1/52; eliminated 10/53 | |
| Joseph Leasing Ltd. | JTLX | Jul-00 | |
| DJLX | added 4/2000; 7/2000 | ||
| Joseph Transportation Co. | JDMX | added 1/2001 | |
| Joseph Transportation de Mexico S.A. de C.V. | ENDX | added 4/2000; 7/2000 | |
| Joseph Transportation Inc. | JTIX | added 4/2000; 7/2000 | |
| JTJX | added 4/2000; 7/2000 | ||
| JTPX | added 4/2000; 7/2000 | ||
| JTSX | added 4/2000; 7/2000 | ||
| DJJX | added 4/2000; 7/2000 | ||
| DJPX | added 4/2000; 7/2000 | ||
| DJRX | added 4/2000; 7/2000 | ||
| DJTX | added 4/2000; 7/2000 | ||
| PSTX | added 4/2000; 7/2000 | ||
| RLMX | added 4/2000; 7/2000 | ||
| SSMX | added 4/2000; 7/2000 | ||
| JoVic Tank Line | JOVX | added 1/62 | |
| Jovita Perez | JPX | Jan-52 | |
| JTM Industries, Inc. | JTMX | added 7/96 | |
| Julius Hyman & Co. | JHCX | eliminated 4/55 | |
| Jumbo Transportation Co. | JMBX | added 4/62; 7/65-10/66; eliminated 1/69 | |
| Juniata Valley R.R. Co. | JVRR | added 1/97; 7/2000 | |