504
- 50401 Mason City
- 50420 Alexander
- 50421 Belmond
- 50423 Britt
- 50424 Buffalo Center
- 50426 Carpenter
- 50428 Clear Lake
- 50430 Corwith
- 50431 Coulter
- 50432 Crystal Lake
- 50433 Dougherty
- 50434 Fertile
- 50435 Floyd
- 50436 Forest City
- 50438 Garner
- 50439 Goodell
- 50440 Grafton
- 50441 Hampton
- 50444 Hanlontown
- 50446 Joice
- 50447 Kanawha
- 50448 Kensett
- 50449 Klemme
- 50450 Lake Mills
- 50451 Lakota
- 50452 Latimer
- 50453 Leland
- 50454 Little Cedar
- 50455 Mc Intire
- 50456 Manly
- 50457 Meservey
- 50458 Nora Springs
- 50459 Northwood
- 50460 Orchard
- 50461 Osage
- 50464 Plymouth
- 50465 Rake
- 50466 Riceville
- 50467 Rock Falls
- 50468 Rockford
- 50469 Rockwell
- 50470 Rowan
- 50471 Rudd
- 50472 Saint Ansgar
- 50473 Scarville
- 50475 Sheffield
- 50476 Stacyville
- 50477 Swaledale
- 50478 Thompson
- 50479 Thornton
- 50480 Titonka
- 50482 Ventura
- 50483 Wesley
- 50484 Woden