| Mavis Stocker Service | Auburn | IN |
| Maxon Marine | Tell City | IN |
| Maxwell Briscoe Motor | New Castle | IN |
| Maxwell Motor | New Castle | IN |
| McCray Memorial Hospital | Kendallville | IN |
| McCray Refrigerator | Kendallville | IN |
| McDougall | Frankfort | IN |
| M.C. Henly | Richmond | IN |
| McHenry-Millhouse Manufacturing | South Bend | IN |
| McWilliams & Company | Linden | IN |
| Mead-Johnson | Evansville | IN |
| Mead Johnson & Company | Mount Vernon | IN |
| Mead Johnson & Company | Evansville | IN |
| Meadow Gold Dairy | Fort Wayne | IN |
| Mead Paper | Cincinnati | IN |
| Medland Steel | Muncie | IN |
| Memorial Hospital | South Bend | IN |
| Mengel | Elkhart | IN |
| Merchants Building | Indianapolis | IN |
| Merchants Distilling | Terre Haute | IN |
| Merchants Electric Light Association | Lafayette | IN |
| Merchants Heat & Light | Indianapolis | IN |
| Merchants Plaza | Indianapolis | IN |
| Mershberger Bros Stone | Pleasant Mills | IN |
| Mesta Machine | New Castle | IN |
| Metallurgical Processing | Fort Wayne | IN |
| Metal & Thermit | East Chicago | IN |
| Methodist Episcopal Hospital | Indianapolis | IN |
| Methodist Hospital | Gary | IN |
| Methodist Hospital | Indianapolis | IN |
| M. H. Hilt | Fort Wayne | IN |
| Michelin | Woodburn | IN |
| M & I Chemicals | East Chicago | IN |
| Michigan City & Northern Indiana Gas | Michigan City | IN |
| Michigan Gas Transmission | Edgerton | IN |
| Michigan Gas Transmission | Montezuma | IN |
| Midland Engineering | Middlebury | IN |
| Midland Engineering | South Bend | IN |
| Midland Steel Products | Muncie | IN |
| Mid States Rubber Product | Princeton | IN |
| Mid States Wire | Crawfordsville | IN |
| Midwestern Gas Transmission | Petersburg | IN |
| Midwest Floor Covering | South Bend | IN |
| Midwest Food Packers | Fowlerton | IN |
| Midwest Insulation | Wabash | IN |
| Midwest Steel | Indianapolis | IN |
| Midwest Steel | Burns Harbor | IN |
| Midwest Steel | Portage | IN |
| Midwest-United Insurance Company Building | Fort Wayne | IN |
| Miles Laboratories | Elkhart | IN |
