| Official Zip Code Name | Monmouth |
| Zip Code State | Illinois |
| Primary County: | Warren |
| Area Code | 309 |
| Current Population: | 37081 |
| Racial Majority: | White 62.49% |
| Median Household Income | $55618 |
| Average Adjusted Gross Income | $89060 |
| Time Zone: | 6 |
| Elevation Range | 763 ft. |
| Area | 142.231 Sqm. |
| Coordinates(Y,X) | 40.910976, -90.652246 |