501--Des Moines, IA (G-M)
502--Des Moines, IA (N-Z)
503--Des Moines, IA (Main)
504--Mason City, IA
505--Fort Dodge, IA
506--Waterloo, IA (Vicinity)
507--Waterloo, IA (Main)
508--Creston, IA
509--Des Moines, IA (NE)
510--Sioux City, IA (East)
511--Sioux City, IA (Main)
512--Sheldon, IA
513--Spencer, IA
514--Carroll, IA
515--Omaha, NE (East)/IA Suburbs
516--N/A
517--N/A
518--N/A
519--N/A
520--Dubuque, IA
521--Decorah, IA
522--Cedar Rapids, IA (A-L)
523--Cedar Rapids, IA (M-Z)
524--Cedar Rapids, IA (Main)
525--Ottumwa, IA
526--Burlington, IA
527--Rock Island, IL (NW)/IA Suburbs
528--Davenport, IA
529--N/A
530--Milwaukee, WI (North)
531--Milwaukee, WI (South)
532--Milwaukee, WI (Main)
533--N/A
534--Racine, WI
535--Madison, WI (Vicinity)
536--N/A
537--Madison, WI (Main)
538--Madison, WI (West)
539--Portage, WI
540--St. Paul, MN (East)/WI Suburbs
541--Green Bay, WI (West)
542--Green Bay, WI (East)
543--Green Bay, WI (Main)
544--Wausau, WI
545--Rhinelander, WI
546--La Crosse, WI
547--Eau Claire, WI
548--Spooner, WI
549--Oshkosh, WI
550--St. Paul, MN (Vicinity)
551--St. Paul, MN (Main)
552--N/A
553--Minneapolis, MN (West/1)
554--Minneapolis, MN (Main)
555--Minneapolis, MN (West/2)
556--North Shore, MN
557--Arrowhead Region, MN
558--Duluth, MN (City & suburbs only)
559--Rochester, MN
560--Mankato, MN
561--Windom, MN
562--Willmar, MN
563--St. Cloud, MN
564--Brainerd, MN
565--Detroit Lakes, MN
566--Bemidji, MN
567--Thief River Falls, MN
568--N/A
569--Washington, DC (Parcel Return)
570--Sioux Falls, SD (Vicinity)
571--Sioux Falls, SD (Main)
572--Watertown, SD
573--Mitchell, SD
574--Aberdeen, SD
575--Pierre, SD
576--Mobridge, SD
577--Rapid City, SD
578--N/A
579--N/A
580--Fargo, ND (Vicinity)
581--Fargo, ND (Main)
582--Grand Forks, ND
583--Devils Lake, ND
584--Jamestown, ND
585--Bismarck, ND
586--Dickinson, ND
587--Minot, ND
588--Williston, ND
589--N/A
590--Billings, MT (Vicinity)
591--Billings, MT (Main)
592--Wolf Point, MT
593--Miles City, MT
594--Great Falls, MT
595--Havre, MT
596--Helena, MT
597--Butte, MT
598--Missoula, MT
599--Kalispell, MT