Illinois - Role: Building
| Odell Building |
| Ogle County Courthouse |
| O'Grady, Mr. J. William de Coursey, House |
| Old Cahokia Courthouse |
| Old Chicago Historical Society Building |
| Old Colony Buildings |
| Old Customhouse |
| Old Danish Church |
| Old Fire Station |
| Old Iroquois County Courthouse |
| Old Main |
| Old Main, Almira College |
| Old Main, Augustana College |
| Old Main Building |
| Old Main, Knox College |
| Old Market House |
| Old McHenry County Courthouse |
| Old Morrison Mill |
| Old Second National Bank |
| Old State Capitol |
| Old Stone Hotel |
| Oliver Building |
| Olmstead Depot |
| Olney Carnegie Library |
| One LaSalle Street Building |
| One Thirty North Eighth Building |
| Orchestra Hall |
| Oregon Public Library |
| Orendorff, Ulysses G., House |
| Original Springs Hotel and Bathhouse |
| Orth House |
| Otis Elevator Company Factory Building |
| Otte, Dennis, Round Barn |
| Oughton, John R., House |
| Our Lady of Lourdes Parish |
| Our Lady of the Holy Rosary Church/Holy Rosary Church |
| Overton, Anthony, Elementary School |
| Overton Hygienic Building |
| Paddock, Colonel George H., House |
| Paddock, Henry I., House |
| Page Brothers Building |
| Page, Henry H., House |
| Paine House |
| Palmer, Col. Gustavus A., House |
| Palmer, Hiram, House |
| Palmolive Building |
| Paradise Missionary Baptist Church |
| Paramount Theatre |
| Paris Carnegie Public Library |
| Paris Elks Lodge No. 812 Building |
| Paris High School and Gymnasium |
| Parlin Library |
| Passionist Fathers Monastery |
| Patten, Charles H., House |
| Pattington Apartments |
| Patton Block Building |
| Patton, John, Log Cabin |
| Paxton Carnegie Public Library |
| Paxton First Schoolhouse |
| Paxton Water Tower and Pump House |
| Peabody, Elizabeth, School |
| Peabody, Francis Stuyvesant, House |
| Peacock Brewery |
| Peck and Hills Furniture Company Warehouse |
| Pekin Federal Building |
| Pelton, Ora, House |
| Pemberton Hall and Gymnasium |
| Pentecost, John L., House |
| Peoples Gas Building |
| Peoples National Bank Building-Fries Building |
| People's State Bank |
| Peoria Automobile Club |
| Peoria City Hall |
| Peoria Waterworks |
| Pere Marquette Hotel |
| Pere Marquette State Park Lodge and Cabins |
| Perkins, Dwight, House |
| Perry County Jail |
| Perry, Joseph Ferris, House |
| Peterstown House |
| Pettingill-Morron House |
| Pettit Memorial Chapel |
| Phelps, Alexis, House |
| Phi Delta Theta Fraternity House |
| Phillips, Alfred, House |
| Phi Mu Sorority House |
| Phoenix Opera House Block |
| Pick, George, House |
| Pickwick Theater Building |
| Pike-Sheldon House |
| Pine Craig |
| Pine Grove Community Club |
| Pinehill |
| Pioneer Gothic Church |
| Pioneer Trust and Savings Bank |
| Pittsfield East School |
| Plainfield Halfway House |
| Plano Hotel |
| Pleasant Grove School |
| Pleasant Home |
Data from United States Park Service and Wikidata
