Founded in 1837, DeKalb County is one of 102 counties in the state of Illinois. Historically, DeKalb County was formed from Kane County. The city of Sycamore is the county seat. With FIPS code of 37, DeKalb County has a population of 100,414 and area of 631 square miles (1,634 km2).
List of all cities in DeKalb County, IL alphabetically
| City/Town | Postal Code | Area Code |
| Clare, IL | 60111 | 815/779 |
| Cortland, IL | 60112 | 815/779 |
| Dekalb, IL | 60115 | 815/779 |
| Esmond, IL | 60129 | 815/779 |
| Fairdale, IL | 60146 | 815/779 |
| Genoa, IL | 60135 | 815/779 |
| Herbert, IL | 60145 | 815/779 |
| Hinckley, IL | 60520 | 815/779 |
| Kingston, IL | 60145 | 815/779 |
| Kirkland, IL | 60146 | 815/779 |
| Malta, IL | 60150 | 815/779 |
| McGirr, IL | 60556 | 815/779 |
| Sandwich, IL | 60548 | 815/779 |
| Shabbona, IL | 60550 | 815/779 |
| Somonauk, IL | 60552 | 815/779 |
| Sycamore, IL | 60178 | 815/779 |
| Valley View, IL | 60145 | 815/779 |
| Waterman, IL | 60556 | 815/779 |