Maine - Significance region: Local
| Moonspring Hermitage |
| Moore, Henry D., Parish House and Library |
| Moore, John, House |
| Moose River Congregational Church |
| Morison, Capt. James, House |
| Morrell House |
| Morrill Homestead |
| Morse & Co. Office Building |
| Morse's Corner School |
| Mortland Family Farm |
| Mount Waldo Granite Works |
| Moyer Site |
| Mt. Battie Tower |
| Mt. Merici Historic District |
| Munroe, Horace, House |
| Murch Family House |
| Nannau |
| Nash, William M., House |
| Nelson Family Farm |
| Newfield (Willowbrook) Historic District |
| New Gloucester Historic District |
| New Sharon Congregational Church |
| Nichols, Capt. John P., House |
| Noble Block |
| Norridgewock Female Academy |
| Norridgewock Free Public Library |
| North Berwick Woolen Mill |
| North Monmouth Library |
| North Newport Christian Church |
| North Waterford Congregational Church |
| North Yarmouth Academy |
| North Yarmouth and Freeport Baptist Meetinghouse |
| Norton House Historic District |
| Norton's Corner School |
| Norton, William F., House |
| Norumbega |
| Norumbega Carriage House |
| Norway Historic District |
| Ntolonapemk, Eastern Surplus Superfund Site |
| Nutting Homestead, The |
| Oakfield Station |
| Oakland Public Library |
| Oaklands |
| Oak Street School |
| Observer Building |
| Odd Fellows Block |
| Off-the-Neck Historic District |
| Ogunquit Memorial Library |
| Old Fire Engine House |
| Old Grist Mill |
| Old Hancock County Buildings |
| Old Post Office |
| Old Post Office |
| Old Red Store |
| Old Schoolhouse |
| Old Tavern |
| Old Town House |
| Old Union Meetinghouse |
| Olsson, Anders and Johanna, Farm |
| Orono Main Street Historic District |
| Orr's Island Meeting House |
| Osgood Family House |
| Osgood, Nathaniel, House |
| Otisfield Town House (Former) |
| Otisfield Town Pound |
| Our Lady of Mount Carmel Catholic Church |
| Oxford Congregational Church and Cemetery |
| Paine Neighborhood Historic District |
| Paris Hill Historic District |
| Paris Public Library |
| Parker House |
| Parson's Bend |
| Parsonsfield Seminary |
| Parsons-Piper-Lord-Roy Farm |
| Parsons, Stephen, House |
| Patten Building |
| Paul Family Farm |
| Peabody-Fitch House |
| Peabody Tavern |
| Peacock Tavern |
| Pebbledene |
| Peck, Bradford, House |
| Pejepscot Paper Company |
| Pejepscot Site |
| Pemaquid Point Light |
| Pendleton, James G., House |
| Pennell Institute |
| Pennellville Historic District |
| Penney, Samuel, House |
| Penobscot Marine Museum |
| Pepperrell, William, House |
| Percy District School House, (Former) |
| Perkins, John, House |
| Perry, Clark, House |
| Perry, William F., House |
| Peters, John, House |
| Pettengill House and Farm |
| Phi Gamma Delta House |
| Philbrook, John M., House |
| Philbrook, Samuel D., House |
Data from United States Park Service and Wikidata
