Iowa - Area of significance: Engineering
| Klondike Bridge |
| Lake City Water Standpipe |
| Lawrence Bridge |
| Le Grand Bridge |
| Le Grand Bridge |
| Lincoln Highway-Raccoon River Rural Segment |
| Little Sioux River Bridge |
| Lock and Dam No. 11 Historic District |
| Lock and Dam No. 16 Historic District |
| Lock and Dam No. 19 Historic District |
| LONESTAR |
| Lower Road Bridge |
| Main Street Bridge |
| Mallory Township Bridge |
| Manning Milwaukee Railroad Trestle |
| Manning Water Tower |
| Marsh Rainbow Arch Bridge |
| Marston Water Tower |
| Matsell Bridge |
| McCoy Polygonal Barn |
| McKenzie, Erza, Round Barn |
| McQuilkin, James Greer, Round Barn |
| Mederville Bridge |
| Meier, Fred W., Round Barn |
| Melan Bridge |
| Mill Creek Bridge |
| Mill Creek Bridge |
| Miller Bridge |
| Miller Round Barn |
| Mill Race Bridge |
| Milwaukee Railroad Shops Historic District |
| Minerva Creek Bridge |
| Monona Township Culvert |
| Moore's Ford Bridge |
| Morgan Bridge |
| "Nebergall ""Knoll Crest"" Round Barn" |
| Nelson, Daniel, House and Barn |
| Nishnabotna River Bridge |
| Nishnabotna River Bridge |
| Nishnabotna River Bridge |
| Nodaway River Bridge |
| North Skunk River Bridge |
| Notbohm Mill Archaeological District |
| Nus, August, Polygonal Barn |
| Oakland Mills Bridge |
| Oakland, William, Round Barn |
| Octagon Barn, Otter Township |
| Octagon Barn, Richland Township |
| Octagon Round Barn, Indian Creek Township |
| Okoboji Bridge |
| Olympic Avenue Bridge |
| Otter Creek Bridge |
| Pine Mill Bridge |
| Plagmann Round Barn |
| Polygonal Barn, Lincoln Township |
| Polygonal Barn, New Oregon Township |
| Polygonal Barn, Van Buren Township |
| Quail Avenue Bridge |
| Quarry Bridge |
| Read Township Culvert |
| Reburn, Thomas, Polygonal Barn |
| Red Bridge |
| Red Bridge |
| River Street Bridge |
| River Street Bridge |
| Roberts Octagon Barn |
| Robin Avenue Bridge |
| Rock Falls Bridge |
| Rockwell City Bridge |
| Roseman Covered Bridge |
| Round Barn, Bruce Township Section 3 |
| Round Barn, Buckingham Township |
| Round Barn, Cooper Township |
| Round Barn, Dubuque Township |
| Round Barn, Millville Township |
| Round Barn, Norway Township |
| Round Barn, Pilot Grove Township |
| Round Barn, Washington Township |
| Round Barn, Washington Township |
| Savanna-Sabula Bridge |
| Secrest Octagon Barn |
| Shell Rock Bridge |
| Shellsburg Bridge |
| Shores-Mueller Company |
| Skunk River Bridge |
| Snake Alley |
| Snider Bridge |
| Southwest Fifth St. Bridge |
| Spotts Round Barn |
| Squaw Creek Bridge 2 |
| Star-Clipper-Canfield Building and Winding Stairway |
| State Street Bridge |
| Stewart Avenue Bridge |
| Steyer Bridge |
| Stock Judging Pavilion |
| Stoe Creek Bridge |
| Storm Creek Bridge |
| Storm Creek Bridge 2 |
| Sumner Bridge |
| Sutliff Bridge |
Data from United States Park Service and Wikidata
