There are 12 properties and one former property listed on the National Register of Historic Places in Warren County. Information about each property can be found at this link on Wikipedia.
Map of Historic Properties
Coal Creek Bridge 
Hoosier Row School 
Indianola Carnegie Library 
Indianola High School 
Lake Ahquabi State Park Picnic Area 
United Presbyterian Church, Summerset 
Polled Hereford Breed Origin Site 
Octagon Barn, Otter Township 
Lake Ahquabi State Park Refectory Area 
Lake Ahquabi State Park Bathhouse Area 
Science Hall, Simpson College 
Palmyra Methodist Episcopal Church 
Former Designation: Warren County Courthouse, Demolished 2019