Population (Persons)
| 2009 |
| Nairobi | 3,138,369 |
| Kiambu | 1,673,785 |
| Kakamega | 1,660,651 |
| Nakuru | 1,603,325 |
| Meru | 1,591,533 |
| Bungoma | 1,375,063 |
| Kisii | 1,263,559 |
| Kilifi | 1,109,735 |
| Machakos | 1,098,584 |
| Mandera | 1,025,756 |
| Kitui | 1,012,709 |
| Kisumu | 968,909 |
| Homa Bay | 963,794 |
| Muranga | 942,581 |
| Mombasa | 939,370 |
| Migori | 917,170 |
| Uasin Gishu | 894,179 |
| Bomet | 891,835 |
| Makueni | 884,527 |
| Turkana | 855,399 |
| Narok | 850,920 |
| Siaya | 842,304 |
| Trans Nzoia | 818,757 |
| Nandi | 752,965 |
| Busia | 743,946 |
| Nyeri | 693,558 |
| Kajiado | 687,312 |
| Wajir | 661,941 |
| Kwale | 649,931 |
| Garissa | 623,060 |
| Nyamira | 598,252 |
| Nyandarua | 596,268 |
| Kericho | 590,690 |
| Baringo | 555,561 |
| Vihiga | 554,622 |
| Kirinyaga | 528,054 |
| Embu | 516,212 |
| West Pokot | 512,690 |
| Laikipia | 399,227 |
| Elgeyo Marakwet | 369,998 |
| Marsabit | 291,166 |
| Taita Taveta | 284,657 |
| Tana River | 240,075 |
| Samburu | 223,947 |
| Isiolo | 143,294 |
| Tharaka Nithi | 130,098 |
| Lamu | 101,539 |