Population and demographics in Nairobi County are highly uneven across the 17 sub‑counties, with huge differences in total residents, density, and age structure. The 2019 Kenya Population and Housing Census recorded Nairobi City County at 4,397,073 residents, making it the most populous and densest county in the country. Within this total, the 17 sub‑counties show striking contrasts between huge, sprawling areas like Embakasi and tiny, hyper‑crowded zones like Mathare.
Overall population and density by sub‑county
The 2019 data for Nairobi’s 17 administrative sub‑counties (also constituencies) show that Embakasi is by far the most populous, while Mathare is the smallest in area but most crowded.
| Sub‑county | Approx. 2019 population | Area (km²) | Pop. density (persons/km²) |
|---|---|---|---|
| Embakasi | 988,808 | large | 2,000–4,000 (estimate) |
| Kasarani | 780,656 | 152.60 | ≈ 5,100 |
| Njiru | 626,482 | — | high |
| Kibra | 185,777 | 12.1 | ≈ 15,300 |
| Langata | 197,489 | 196.8 | 911 |
| Westlands | — | 72.4 | moderate |
| Makadara | 189,536 | 13.0 | ≈ 14,600 |
| Kamukunji | 268,276 | 12.0 | ≈ 22,400 |
| Mathare | 206,564 | 3.0 | ≈ 68,900 |
These figures show that Embakasi alone accounts for about 22.5% of Nairobi’s population, while Mathare, at only 3 km², packs over 200,000 residents with the highest density in the county.
Demographic patterns by sub‑county type
Demographics in Nairobi vary by zone:
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Large, mixed‑income suburbs (Embakasi, Kasarani, Njiru):
These sub‑counties host large youth populations, significant numbers of low‑ and middle‑income households, and many rental units, giving them high dependency and informal‑sector employment shares. -
High‑density informal‑settlement zones (Kibra, Mathare, parts of Embakasi East/South):
These areas have very young age structures, with a high proportion under 25, and many one‑room residences supporting extended families. -
Middle‑income and planned estates (Roysambu, parts of Langata, parts of Westlands):
These sub‑counties tend to have slightly older age profiles, more formal‑sector workers, and higher ownership of amenities such as private vehicles and improved sanitation. -
Inner‑city and industrial zones (Starehe, Makadara, Kamukunji):
These areas combine daytime commercial populations with residents in low‑cost housing and face housing‑stock shortages, leading to high population‑to‑service ratios for water, health, and waste management.
Household and living‑conditions indicators
Nairobi as a whole has 1,506,888 households and an average household size of 2.9 persons, the smallest in Kenya, indicating a relatively high number of small‑family and single‑occupancy dwellings. Within sub‑counties, variations appear:
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High‑density informal zones such as Kibra, Mathare, and parts of Makadara often report higher effective household density because multiple families share single rooms.
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Planned estates in Westlands, Langata, and Kasarani tend to have larger individual units but fewer people per structure, translating into lower effective density even when land‑area figures are modest.
Relating population to governance and planning
Because Nairobi County is small in land area (about 696 km²) but huge in population, the distribution of residents across the 17 sub‑counties directly shapes county planning and resource allocation. High‑population zones (Embakasi, Kasarani, Njiru) receive larger shares of:
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Health‑facility and school‑expansion budgets.
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Road‑and‑drainage works in the County Integrated Development Plans (CIDPs).
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Security and emergency‑service deployment to match the massive daytime and night‑time populations.
Conversely, very dense but small sub‑counties like Mathare and parts of Kibra are prioritised for slum‑upgrading programs, water‑and‑sanitation upgrades, and housing‑rehabilitation because of their extreme crowding and poverty levels.
Where to find detailed ward‑level data
For deeper demographic analysis (age, sex, education, disability, employment), the Kenya National Bureau of Statistics publishes wards‑level tables within the “Population by County and Sub‑County” censuses. These ward‑level datasets break each of Nairobi’s 17 sub‑counties into 5 wards, allowing anyone to see:
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How population and household structures differ between, say, Kariobangi South (Embakasi/Kasarani) and South C (Langata).
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Which wards have the highest youth unemployment, dependency ratios, or informal‑sector workers, informing NGO and private‑sector targeting.
In short, the population and demographics by sub‑county in Nairobi County reveal a city of dramatic contrasts: expansive low‑ to middle‑income suburbs next to tiny, ultra‑dense informal settlements, all crammed into a small territory. Understanding these patterns is essential for anyone planning housing, services, marketing campaigns, or social‑development projects in the capital.
