18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Key West | 1 | 24,960 | 26,437 | -1.11% | 4,458 | 6 | City |
| Key West | 2 | 24,960 | 26,360 | -1.11% | 4,458 | 6 | City |
| Key Largo | 3 | 12,418 | 9,670 | 1.07% | 1,031 | 12 | CDP |
| Marathon | 4 | 10,084 | 9,734 | 0.45% | 1,194 | 8 | City |
| Marathon | 5 | 10,084 | 9,857 | 0.45% | 1,194 | 8 | City |
| Islamorada, Village Islands | 6 | 6,985 | 7,127 | -0.4% | 1,083 | 6 | Village |
| Islamorada, Village Islands | 7 | 6,985 | 7,122 | -0.4% | 1,083 | 6 | Village |
| Stock Island | 8 | 4,725 | 4,692 | 1.13% | 5,645 | 1 | CDP |
| Big Pine Key | 9 | 4,564 | 4,853 | 0.44% | 447 | 10 | CDP |
| Big Coppitt Key | 10 | 3,371 | 2,644 | 1.84% | 2,921 | 1 | CDP |
| Cudjoe Key | 11 | 2,357 | 2,157 | 1.73% | 456 | 5 | CDP |
| Tavernier | 12 | 2,292 | 1,980 | 0.44% | 912 | 3 | CDP |
| North Key Largo | 13 | 1,278 | 884 | 0.16% | 69 | 19 | CDP |
| Duck Key | 14 | 758 | 761 | 1.2% | 1,265 | 1 | CDP |
| Key Colony Beach | 15 | 739 | 787 | -1.34% | 1,680 | 0 | City |
| Key Colony Beach | 16 | 739 | 786 | -1.34% | 1,680 | 0 | City |
| Layton | 17 | 206 | 216 | -0.96% | 1,272 | 0 | City |
| Layton | 18 | 206 | 216 | -0.96% | 1,272 | 0 | City |
Key West is the largest city in Monroe County, with a population of 24,960.
Layton is the smallest city in Monroe County, with a population of 206.
There are 18 cities in Monroe County, Florida.