| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Crystal Lake | 1 | 42,601 | 40,246 | 0.74% | 2,244 | 19 | City |
| Algonquin | 2 | 31,039 | 29,668 | 0.7% | 2,475 | 13 | Village |
| Huntley | 3 | 29,310 | 27,763 | 0.61% | 2,000 | 15 | Village |
| Woodstock | 4 | 25,796 | 25,646 | 0.22% | 1,956 | 13 | City |
| Cary | 5 | 17,982 | 17,803 | 0.28% | 2,760 | 7 | Village |
| Harvard | 6 | 9,492 | 9,458 | -0.13% | 1,133 | 8 | City |
| Marengo | 7 | 7,772 | 7,553 | 0.45% | 873 | 9 | City |
| Wonder Lake | 8 | 5,920 | 4,004 | 5.85% | 1,179 | 5 | Village |
| Spring Grove | 9 | 5,542 | 5,469 | 0.29% | 612 | 9 | Village |
| Fox River Grove | 10 | 4,893 | 4,694 | 0.25% | 2,858 | 2 | Village |
| Richmond | 11 | 2,123 | 2,083 | 0.43% | 495 | 4 | Village |
| Prairie Grove | 12 | 1,937 | 1,954 | -0.1% | 319 | 6 | Village |
| Hebron | 13 | 1,395 | 1,386 | 0.22% | 713 | 2 | Village |
| Bull Valley | 14 | 1,130 | 1,131 | -0.09% | 115 | 10 | Village |
| Ringwood | 15 | 829 | 838 | -0.12% | 215 | 4 | Village |
| Union | 16 | 719 | 550 | 5.12% | 860 | 1 | Village |
| Greenwood | 17 | 313 | 317 | -0.32% | 118 | 3 | Village |
Crystal Lake is the largest city in McHenry County, with a population of 42,601.
Greenwood is the smallest city in McHenry County, with a population of 313.
There are 17 cities in McHenry County, Illinois.