| Kocaeli Subregion | |
| Native Name: | Kocaeli Alt Bölgesi |
| Native Name Lang: | tr |
| Settlement Type: | Subregion |
| Subdivision Type: | Country |
| Subdivision Name: | Turkey |
| Subdivision Type1: | Region |
| Subdivision Name1: | East Marmara |
| Area Total Km2: | 20,402 |
| Population Total: | 3,448,702 |
| Population As Of: | 2013 |
| Population Density Km2: | auto |
| Population Rank: | 6th |
| Population Urban: | 3,148,994 |
| Population Rural: | 299,708 |
The Kocaeli Subregion (Turkish: Kocaeli Alt Bölgesi) (TR42) is a statistical subregion in Turkey.