Wisconsin - Significance region: Local
| Omro Downtown Historic District |
| Omro High School, Annex and Webster Manual Training School |
| Omro Village Hall and Engine House |
| Oneida County Courthouse |
| Onion River Flouring Mill/Grist Mill |
| Opera Hall Block |
| Orchard Street Historic District |
| Oregon High School |
| Oregon Masonic Lodge |
| Oregon Water Tower and Pump House |
| Orfordville Depot |
| Oriental Theatre |
| Orpheum Theater |
| Orth, Phillip, Boathouse |
| Orton Park |
| Orton Park Historic District |
| Osceola Commercial Historic District |
| Oshkosh Grand Opera House |
| Oshkosh State Normal School Historic District |
| Osprey Site |
| Ottawa House |
| Otter Spring House |
| Ott, John George, House |
| Ott, Will, House |
| Our Lady of Loretto Roman Catholic Church and Cemetery |
| Our Lady of Sorrows Chapel |
| Outlet Mound |
| Oviatt House |
| Owen High School |
| Owen, John and Margaret, House |
| Owen, John S., House |
| Owen Park Bandshell |
| Owen, Ray S. and Theo P., House |
| Pabst Brewery Saloon |
| Paepke, Henry, House |
| Paine Lumber Company Historic District |
| Painesville Chapel |
| Palmyra Boy Scout Cabin |
| Palo, John and Justina, Homestead |
| Pangborn, J. L., House |
| Panther Intaglio Effigy Mound |
| Paoli Co-Operative Creamery Company Plant |
| Paoli Mills |
| Paramount Knitting Company Mill |
| Pardeeville Presbyterian Church |
| Parker, Dwight T., Public Library |
| Park Falls Post Office |
| Parkin Ice Cream Company |
| Park Street Historic District |
| Parkview Historic District |
| Pattison, Martin, House |
| Payne-Craig House |
| Payne Hotel |
| Peacock Inn |
| Pearl and Grand Avenue Historic District |
| Peck, Clarence, Residence |
| Peck, George W., Row House |
| Peckham Junior High School |
| Peck, Walter L., House |
| Pelican Lake Hotel |
| Pepin County Courthouse and Jail |
| Perry, Melvin W. and Mary, House |
| Perry, Ralph P., House |
| Peshtigo Fire Cemetery |
| Peshtigo Reef Light |
| Peters, George, House |
| Peterson, Peter, House |
| Phillips High School |
| Phipps, William H., House |
| Phlaum-McWilliams Mound Group |
| Physical Education Building/La Crosse State Normal School |
| Pierce, Carrie, House |
| Pierce County Courthouse |
| Pioneer Block |
| Pipe School |
| Pittsburgh Plate Glass Enamel Plant |
| Plankinton-Wells-Water Street Historic District |
| Pleasant Hill Residential Historic District |
| Plough Inn |
| Plum Grove Primitive Methodist Church |
| Plymouth Post Office |
| Pokrandt Blacksmith Shop |
| Polk County Courthouse |
| Pollock, William E., Residence |
| Polson, Mrs. Richard, House |
| Pomeroy and Pelton Tobacco Warehouse |
| Pomeroy, L. A., House |
| Pond, Daniel, Farmhouse |
| Portage Industrial Waterfront Historic District |
| Portage Retail Historic District |
| Portage Street Historic District |
| Porter, J. K., Farmstead |
| Porter, Walworth D., Duplex Residence |
| Port Washington Downtown Historic District |
| Port Washington Fire Engine House |
| Port Washington Light Station |
| Port Washington North Breakwater Light |
| Potawatomi State Park Observation Tower |
| Potosi Badger Huts Site |
| Potosi Brewery |
Data from United States Park Service and Wikidata
