| Name | Railroad, # | Builder, s/n | Build date | Whyte type | Notes |
|---|---|---|---|---|---|
| I. Acken | NJR&T | Rogers 294 | 12/1851 | 4-4-0 | |
| I. B. Futvoye | CV 40 | Souther | 1852 | 4-4-0 | Ex-Iron Horse; rebuilt and renamed Governor Smith in 1866; sold 1884 to SS&C; returned and renamed back to I. B. Futvoye; scrapped 1895. |
| I. E. James | V&T 9 | Baldwin 2199 | 1871 | 2-4-0 | Sold 1907; scrapped 1946. |
| I. S. Roberts | H&TC 34 | Rogers | 4-4-0 | ||
| I. V. Baker | R&S 31 | Schen 435 | 1867 | 4-4-0 | To D&H 126; rn 379; off roster by 1902. |
| I. W. Dow | NLN 17 | Manch | 1872 | 4-4-0 | Rn 1892 #167; transferred to CV 23. |
| I. W. McDade | H&TC 9 | Schen 452 | 6/1867 | 4-4-0 | Rn 1885 #9; off roster by 1901. |
| I. W. McDade | WC 1 | Rogers 1416 | 11/1866 | 4-4-0 | Became H&TC #41 3/11/1869. |
| Idaho | CP 17 | Mason 224 | 2/1866 | 4-6-0 | Exploded 1 mile east of summit tunnel (Donner Pass?) 1/2/1879; scr. |
| Idaho | U&N 5 | Grant | 9/1872 | 4-6-0 | Rn #286; scr c. 1886. |
| Idaho | UP 7 | Schen | 1865 | 4-4-0 | Rn 1882 #574; rb 1882; scr 1896. |
| Illinois | Milholland | 1852 | |||
| Independence | M&SC | Rogers 255 | 4/1851 | 4-4-0 | |
| Independencia | FCUY 53 | Baldwin 20970 | 9/1902 | 0-4-0 | Ex-FCM&P #13; scr 1925. |
| Indiana | PRR | Baldwin | 1849 | 4-2-2 | |
| Indianapolis | P&I 6 | Rogers 1091 | 7/1863 | 4-4-0 | To IP&C 1864; to WStL&P #506 1881. |
| Indian Chief | B&O | 1833 | 0-4-0 | Rn Traveller. | |
| Industry | WP I | Norris-L 14 | 1864 | 4-4-0 | off roster by 1878; first coal burner on West Coast; to CP 6/1870 2nd #25. |
| Ingleside | SA&AP 15 | Baldwin 8298 | 12/1886 | 0-6-0 | Off roster by 1917. |
| International | C&NF 3 | Rogers 375 | 2/1853 | 4-4-0 | 6 ft gauge. |
| Inyo | B&B 2 | Baldwin | 2-6-0 | ||
| Inyo | V&T 22 | Baldwin 3693 | 1875 | 4-4-0 | Sold 3/1937 to Paramount Pictures. |
| Ionic | LNA&C 24 | Hinkley 463 | 8/1853 | 4-4-0 | Ex-Reindeer; ex-NA&S Woodville. |
| Iowa | M&SP 71 | Norris | 1848 | 4-4-0 | Ex-M&M #1 Bob Ellis, the first locomotive to operate in Wisconsin. |
| Ira Brownell | R&S | S & Jackson | 1863 | 4-4-0 | Rn 24; became D&H #119; scr 1881. |
| Ira E. Shuman | A&S 19 | Dickson 37 | 1868 | 4-4-0 | |
| Iris | Winans 59 | Camelback locomotive. | |||
| Irolo | FCHN 4 | Porter 837 | 7/1887 | 0-4-4T | NG; retired by 1908. |
| Irolo | Irolo 2 | Baldwin 6080 | 3/1882 | 2-6-0 | Became FCI (Mexico) #27 in 1889; rn #25; NG. |
| Iron City | PRR | Baldwin | 1854 | 0-8-0 | |
| Iron Cliff | C&NW 139 | Hinkley 728 | 4-4-0 | ||
| Iron Horse | CV 40 | Souther | 1852 | 4-4-0 | Renamed 1885 to I. B. Futvoye; rn Gov. Smith 3/1869; rb 1/1866. |
| Iron Ivan | AC 7 | Baldwin 18595 | 1/1901 | 2-6-2 | Originally built for the McCloud River Railroad; s 1937 to Amador Central; pulled the last steam-powered train on in Amador County, California, on a trip between Ione and Martell in 1956. Preserved on static display in Ione, California. |
| Ironsides | Baldwin | 1832 | |||
| Iroquois | CV 15 | H & Drury | 1849 | 4-4-0 | Rb 4/13/1861; rn 3/1869 Woodstock; rn 3/1871 Express; sold 4/1/1884 to SS&C. |
| Iroquois | RGSW 32 | Baldwin 8699 | 8/1887 | 2-8-0 | Ex-Rio Grande & Pagosa Springs. |
| Irvington | HR | Lawrence | 1856 | 4-4-0 | Designed by Alba F. Smith, then superintendent of the Hudson River Railroad. |
| Isaac Lees | TT 23 | Grant | 3/1882 | 2-6-0 | NG; sold 8/1888 to William Black, Brinkley, Ar. |
| Isaac N. Seymour | D&HG 5 | Jersey | 1866 | 4-4-0 | Exploded 3/10/1879 at Carbondale; sold to Dickson Loco Works. |
| Isaac Scott | M&W | Rogers 146 | 10/1848 | 4-4-0 | |
| Isaac Sherman | M&SP 57 | Rogers 1360 | 4/1866 | 4-4-0 | Rn #220 in 1898; rn # 1223 in 1899; rn 1416; off roster by 1907. |
| Ithaca | C&Su | Rogers 250 | 2/1851 | 4-4-0 | |
| Ithaca | I&A | Baldwin | 1871 | 2-4-0 |