| ZIP Code | ZIP Code Place Name | County | ZIP Code Type |
|---|---|---|---|
| 50401 | Mason City | Cerro Gordo County | Standard |
| 50402 | Mason City | Cerro Gordo County | PO Box |
| 50428 | Clear Lake | Cerro Gordo County | Standard |
| 50433 | Dougherty | Cerro Gordo County | Standard |
| 50434 | Fertile | Worth County | Standard |
| 50440 | Grafton | Worth County | Standard |
| 50444 | Hanlontown | Worth County | Standard |
| 50446 | Joice | Worth County | Standard |
| 50448 | Kensett | Worth County | Standard |
| 50450 | Lake Mills | Winnebago County | Standard |
| 50456 | Manly | Worth County | Standard |
| 50457 | Meservey | Cerro Gordo County | Standard |
| 50458 | Nora Springs | Floyd County | Standard |
| 50459 | Northwood | Worth County | Standard |
| 50464 | Plymouth | Cerro Gordo County | Standard |
| 50467 | Rock Falls | Cerro Gordo County | Standard |
| 50468 | Rockford | Floyd County | Standard |
| 50469 | Rockwell | Cerro Gordo County | Standard |
| 50472 | Saint Ansgar | Mitchell County | Standard |
| 50475 | Sheffield | Franklin County | Standard |
| 50477 | Swaledale | Cerro Gordo County | Standard |
| 50479 | Thornton | Cerro Gordo County | Standard |
| 50482 | Ventura | Cerro Gordo County | Standard |