| Year |
Length (miles) |
Route (start to finish) |
| 1973 |
412 |
Sioux City, Storm Lake, Fort Dodge, Ames, Des Moines, Williamsburg, and Davenport |
| 1974 |
422 |
Council Bluffs, Atlantic, Guthrie Center, Camp Dodge, Marshalltown, Waterloo, Monticello, and Dubuque |
| 1975 |
450 |
Hawarden, Cherokee, Lake View, Boone, Newton, Sigourney, Mount Pleasant, and Fort Madison |
| 1976 |
430 |
Sidney, Red Oak, Harlan, Jefferson, Nevada, Grinnell, Iowa City, and Muscatine |
| 1977 |
400 |
Onawa, Ida Grove, Laurens, Algona, Clear Lake, New Hampton, Decorah, and Lansing |
| 1978 |
440 |
Sioux City, Storm Lake, Humboldt, Iowa Falls, Vinton, Mount Vernon, Maquoketa, and Clinton |
| 1979 |
480 |
Rock Rapids, Spencer, Rockwell City, Story City, Tama, Fairfield, Wapello, and Burlington |
| 1980 |
468 |
Glenwood, Atlantic, Carroll, Perry, Webster City, Waverly, Elkader, and Guttenberg |
| 1981 |
490 |
Missouri Valley, Mapleton, Lake City, Greenfield, Leon, Centerville, Keosauqua, and Keokuk |
| 1982 |
523 |
Akron, Cherokee, Estherville, Forest City, Charles City, Independence, Tipton, and Davenport |
| 1983 |
492 |
Onawa, Harlan, Guthrie Center, Ames, Clarion, Grundy Center, Manchester, and Dubuque |
| 1984 |
474 |
Glenwood, Shenandoah, Creston, Adel, Pella, Ottumwa, Mount Pleasant, and Burlington |
| 1985 |
540 |
Hawarden, Sibley, Emmetsburg, Humboldt, Mason City, Waterloo, Monticello, and Clinton |
| 1986 |
479 |
Council Bluffs, Red Oak, Audubon, Perry, Eldora, Belle Plaine, Washington, and Muscatine |
| 1987 |
437 |
Onawa, Denison, Storm Lake, Fort Dodge, Forest City, Osage, West Union, and Guttenberg |
| 1988 |
433 |
Sioux City, Ida Grove, Carroll, Boone, Des Moines, Oskaloosa, Fairfield, and Fort Madison |
| 1989 |
479 |
Glenwood, Clarinda, Atlantic, Jefferson, Story City, Cedar Falls, Dyersville, and Bellevue |
| 1990 |
495 |
Sioux Center, Spencer, Algona, Hampton, Oelwein, Cedar Rapids, Washington, and Burlington |
| 1991 |
432 |
Missouri Valley, Atlantic, Winterset, Knoxville, Grinnell, Amana, Anamosa, and Bellevue |
| 1992 |
494 |
Glenwood, Shenandoah, Bedford, Osceola, Des Moines, Oskaloosa, Mount Pleasant, and Keokuk |
| 1993 |
525 |
Sioux City, Sheldon, Emmetsburg, Clarion, Osage, Decorah, Manchester, and Dubuque |
| 1994 |
511 |
Council Bluffs, Harlan, Carroll, Perry, Marshalltown, Marion, Maquoketa, and Clinton |
| 1995 |
493 |
Onawa, Lake View, Fort Dodge, Iowa Falls, Tama, Sigourney, Coralville, and Muscatine |
| 1996 |
437 |
Sioux Center, Sibley, Estherville, Lake Mills, Charles City, Cresco, Fayette, and Guttenberg |
| 1997 |
464 |
Missouri Valley, Red Oak, Creston, Des Moines, Chariton, Bloomfield, Fairfield, and Fort Madison |
| 1998 |
488 |
Hawarden, Cherokee, Rockwell City, Boone, Eldora, Cedar Falls, Monticello, and Sabula |
| 1999 |
487 |
Rock Rapids, Spencer, Algona, Clear Lake, Waverly, Decorah, Manchester, and Bellevue |
| 2000 |
450 |
Council Bluffs, Harlan, Greenfield, Ankeny, Knoxville, Ottumwa, Washington, and Burlington |
| 2001 |
506 |
Sioux City, Storm Lake, Denison, Atlantic, Perry, Grinnell, Coralville, and Muscatine |
| 2002 |
525 |
Sioux Center, Cherokee, Emmetsburg, Forest City, Charles City, Oelwein, Anamosa, and Bellevue |
| 2003 |
495 |
Glenwood, Shenandoah, Bedford, Osceola, Oskaloosa, Bloomfield, Mount Pleasant, and Fort Madison |
| 2004 |
490 |
Onawa, Lake View, Fort Dodge, Iowa Falls, Marshalltown, Hiawatha, Maquoketa, and Clinton |
| 2005 |
485 |
Le Mars, Sheldon, Estherville, Algona, Northwood, Cresco, West Union, and Guttenberg. |
| 2006 |
444 |
Sergeant Bluff, Ida Grove, Audubon, Waukee, Newton, Marengo, Coralville, and Muscatine. |
| 2007 |
479 |
Rock Rapids, Spencer, Humboldt, Hampton, Cedar Falls, Independence, Dyersville, and Bellevue |
| 2008 |
471 |
Missouri Valley, Harlan, Jefferson, Ames, Tama/Toledo, North Liberty, Tipton, and Le Claire |
