Illinois - Significance region: Local
| Old Main Building |
| Oliver Building |
| Olmstead Depot |
| Olney Carnegie Library |
| Olympia Fields Country Club |
| One LaSalle Street Building |
| One Thirty North Eighth Building |
| Oregon Commercial Historic District |
| Oregon Public Library |
| Otis Elevator Company Factory Building |
| Ottawa Commercial Historic District |
| Ottawa East Side Historic District |
| Otte, Dennis, Round Barn |
| Ouilmette North Historic District |
| Our Lady of Lourdes Parish |
| Our Lady of the Holy Rosary Church/Holy Rosary Church |
| Overton, Anthony, Elementary School |
| Overton Hygienic Building |
| Pacesetter Gardens Historic District |
| Paddock, Colonel George H., House |
| Paddock, Henry I., House |
| Page, Henry H., House |
| Paine House |
| Palestine Commercial Historic District |
| Palmer, Col. Gustavus A., House |
| Palmer, Hiram, House |
| Palmer Park |
| Palmolive Building |
| Paradise Missionary Baptist Church |
| Paris Carnegie Public Library |
| Paris Elks Lodge No. 812 Building |
| Paris High School and Gymnasium |
| Parkway Garden Homes |
| 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, Estate |
| Peacock Brewery |
| Peck and Hills Furniture Company Warehouse |
| Pekin Federal Building |
| Pelton, Ora, House |
| Pennsylvania Avenue Historic District |
| Pentecost, John L., House |
| Peoples National Bank Building-Fries Building |
| People's State Bank |
| Peoria Automobile Club |
| Peoria Cordage Company |
| Peoria Mineral Springs |
| Peoria Warehouse Historic District |
| Pere Marquette Hotel |
| Pere Marquette State Park Lodge and Cabins |
| Perry County Jail |
| Perry, Joseph Ferris, House |
| Phelps, Alexis, House |
| Phi Delta Theta Fraternity House |
| Phillips, Alfred, House |
| Phi Mu Sorority House |
| Phoenix Opera House Block |
| Pike-Sheldon House |
| Pilsen Historic District |
| Pine Grove Community Club |
| Piney Creek Site |
| Piney Creek South Site |
| Piney Creek West Site |
| Pioneers, The |
| Pioneer Trust and Savings Bank |
| Pittsfield Historic District |
| Plainfield Halfway House |
| Plano Hotel |
| Pleasant Grove School |
| Poinsetta Apartments |
| Point School |
| Polish National Alliance Headquarters |
| Polish Roman Catholic Union of America |
| Polo Independent Order of Odd Fellows Lodge No. 197 |
| Pontiac City Hall and Fire Station |
| Pope Brace Company Building |
| Portage Park |
| Portage Park Bungalow Historic District |
| Post House |
| Potter and Barker Grain Elevator |
| Potter House |
| Power Farmstead |
| Prairie Dell Meetinghouse |
| Price-Prather House |
| Price/Wheeler House |
| Princeton North Main Street Historic District |
| Princeton South Main Street-Courthouse Square Historic District |
| Proctor Building |
| Proctor, John C., Recreation Center |
| Produce Terminal Cold Storage Company Building |
| Promontory Point |
| Public Service Building |
Data from United States Park Service and Wikidata
