| JP Austin Associated | Davenport | IA |
| Junior High School | Red Oak | IA |
| J.W. Davis | Bettendorf | IA |
| Kahl Building | Davenport | IA |
| Kalo Brick & Tile | Kalo | IA |
| Kenwood Methodist Church | Cedar Rapids | IA |
| Keokuk County Heating Plant | Sigourney | IA |
| Keokuk Railway & Power | Keokuk | IA |
| Keokuk Steel Castings | Keokuk | IA |
| Killian's Department Store-Tea Room | Cedar Rapids | IA |
| Kings Concrete | Cedar Rapids | IA |
| Kings Crown Plaster | Cedar Rapids | IA |
| Kiowa | Marshalltown | IA |
| Kirkwood Motel | Des Moines | IA |
| Kohrs Cold Storage | Davenport | IA |
| Kromer Produce | Mason City | IA |
| Kromer Produce | Waterloo | IA |
| Lake Shore Tire & Rubber | Des Moines | IA |
| Land O Lakes Cooperative | Sheldon | IA |
| Lansing Power Plant | Lansing | IA |
| Lattiner P.M. Manufacturing | Cedar Rapids | IA |
| L.C. Harberger | Keokuk | IA |
| Le Claire Manufacturing | Le Claire | IA |
| Le Claire Manufacturing | Le Mars | IA |
| Legion Hall | West Branch | IA |
| Legion Hall | Ottumwa | IA |
| Lehigh Cement | Mason City | IA |
| Lehigh Portland Cement | Mason City | IA |
| Lehy Bridge & Tile | Fort Dodge | IA |
| L.H. Kurtz | Des Moines | IA |
| Linde Air Products | Davenport | IA |
| Linde Air Products | Des Moines | IA |
| Link Belt | Cedar Rapids | IA |
| Lippert Bros. | Marshalltown | IA |
| Little Ralph | Davenport | IA |
| L & L Insulation | Des Moines | IA |
| Longview Fibre | Cedar Rapids | IA |
| Louisa Des Moines Drainage District | Oakville | IA |
| Low Rent Housing | Des Moines | IA |
| Lusk Candy | Davenport | IA |
| Lutheran Hospital | Des Moines | IA |
| Lyons & Carnahan | Muscatine | IA |
| Machine Products | Corydon | IA |
| Maizwood Products | Dubuque | IA |
| Malek Theatre | Independence | IA |
| Manly High School | Manly | IA |
| Manson High School | Manson | IA |
| Maquoketa Light & Power | Maquoketa | IA |
| Marian Health Center | Sioux City | IA |
| Marion High School | Marion | IA |
