Iowa - Criteria: C (architecture/engineering)
| Clark, Gerome, House |
| Clark House |
| Clark Round Barn |
| Claussen, William, House |
| Clay County Courthouse |
| Clayton County Courthouse |
| Clayton School |
| Clemens Automobile Company Building |
| Clermont Public School |
| Clifton |
| Clinton County Courthouse |
| Clinton High School and Public Library |
| Clinton Public Library |
| Close House |
| CM and StP Railroad Underpass |
| Coal Creek Bridge |
| Coal Ridge Baptist Church and Cemetery |
| Cody Homestead |
| Cody Road Historic District |
| Coggon Public School |
| Coldwater Church of the Brethren |
| Colfax Spring City Commercial Historic District |
| College Block Building |
| College Corner Commercial Historic Business District |
| College Green Historic District |
| College Hall |
| College Square Historic District |
| Collegiate Neighborhood Historic District |
| Collins-Bond House |
| Collins House |
| Colonials Club House |
| Columbia Avenue Historic District |
| Columbus Junction School 1882-1920 |
| Conant's Cabin and Park |
| Conger, Jonathan Clark, House |
| Congregational Church of Iowa City |
| Consistory Building No. 2 |
| Cook, Clarissa, Home for the Friendless |
| Cook Farm |
| Cooley-Whitney House |
| Cooper, George and Margaret, House |
| Cooper, George, House |
| Copeland, George, House |
| Coralville Public School |
| Cork Hill District |
| Cornelia Lake Bridge |
| Cornell College-Mount Vernon Historic District |
| Cornell, W. J. and Nettie J., House |
| Corning Commercial Historic District |
| Corpus Christi Church |
| Cottage at 1514 and 1516 W. Second Street |
| Cottage at Rock and Dubuque Streets |
| Cottage Grove Avenue Presbyterian Church |
| Cotton Theater |
| Council Bluffs Free Public Library |
| County Line Bridge |
| Court Avenue Bridge |
| Court Hill Historic District |
| Courthouse Square Historic District |
| Cowles, George H and Alice Spaulding, House |
| Crane Building |
| Crapo Park and Arboretum Historic District |
| Craven, J. D., Women's Relief Corps Hall |
| Crawford County Courthouse |
| Crawford House |
| Crescent Warehouse Historic District |
| Cretsinger, John, House |
| Crozier, J.T. and Mollie, House |
| C.S.P.S. Hall |
| Cundill Block |
| Cunningham Bridge |
| Currier House |
| Curtis, George M., House |
| Cutler-Donahue Covered Bridge |
| Dahlonega School #1 |
| Dallas County Courthouse |
| Damour, William and Sue, House |
| Darling, Jay Norwood and Genevieve Pendleton, House |
| Dau, William C. and Hertha, House |
| Davenport Bag and Paper Company Building |
| Davenport City Hall |
| Davenport Hose Station No. 3 |
| Davenport Hotel |
| Davenport Village |
| Davenport Water Co. Pumping Station No. 2 |
| Davidson Building |
| Davis County Courthouse |
| Davison, Abner, House |
| Davis, Timothy, House |
| Dawley House |
| Decatur County Courthouse |
| Decker House Hotel |
| Decorah Municipal Bathhouse and Swimming Pool |
| DeFries House, Barn and Carpenter Shop |
| Delaware County Courthouse |
| Delmar Calaboose |
| Democrat Building |
| Des Moines Art Center |
| Des Moines Building |
| Des Moines County Court House |
Data from United States Park Service and Wikidata
