| National Friction Products | Logansport | IN |
| National Fruit Juice | Lafayette | IN |
| National Guard Armory | Vincennes | IN |
| National Handle | Fort Wayne | IN |
| National Heat Treating | Fort Wayne | IN |
| National Home for Disabled Volunteer Soldiers | Marion | IN |
| National Home For Disabled Volunteer Soldiers | Marion | IN |
| National Light, Heat & Power | Bloomington | IN |
| National Malleable Casting | Indianapolis | IN |
| National Military Home | Marion | IN |
| National Rolling Mills | Vincennes | IN |
| National Standard | Mishawaka | IN |
| National Starch & Chemical | Indianapolis | IN |
| National Steel | Portage | IN |
| National Tile | Anderson | IN |
| National Tube | Gary | IN |
| National Veneer & Lumber | Seymour | IN |
| Natural Gas Manufacturing Plant | Shoals | IN |
| Natural Gas Manufacturing Plant | Alexandria | IN |
| Naval Surface Warfare Center Crane Division | Crane | IN |
| Neils Science Lab | Mishawaka | IN |
| New Albany Veneering | New Albany | IN |
| New Albany Water Works | New Albany | IN |
| New Castle Light, Heat, & Power | New Castle | IN |
| New Castle Machine Plant | New Castle | IN |
| New Castle State Hosp | New Castle | IN |
| New Corning Glass Plant | Bluffton | IN |
| New Energy Company Of Indiana | South Bend | IN |
| New Energy Ethanol Power Plant | South Bend | IN |
| New Jersey Zinc | East Chicago | IN |
| Newlon Metals | Kokomo | IN |
| Newport Army Ammunition Plant | Newport | IN |
| New State Farm Insurance Building | Lafayette | IN |
| New Waterworks Building | Bloomington | IN |
| New York Central Railroad | La Porte | IN |
| New York Central System | Elkhart | IN |
| New York Central System | Indianapolis | IN |
| Nibco | Elkhart | IN |
| Nichols Engineering & Research | Indianapolis | IN |
| Nicholson File | Anderson | IN |
| Nipsco | Hammond | IN |
| N Kok Hs | Indianapolis | IN |
| Noah M. Simmons | Indianapolis | IN |
| Noblesville Heat, Light & Power | Noblesville | IN |
| Noblesville Junior High School | Noblesville | IN |
| Noblesville Milling | Indianapolis | IN |
| Noblesville Milling | Noblesville | IN |
| Noblesville Power Plant | Noblesville | IN |
| Noblitt Sparks Industries | Columbus | IN |
| Nordyke & Marmon | Noblesville | IN |
