Specifically, it is an official language in:
* Kenya
* Tanzania
* Uganda
It is also spoken as a second language in many other countries in the region, including:
* Rwanda
* Burundi
* Democratic Republic of Congo
* Mozambique
* Somalia
* Comoros
* Seychelles
* Malawi
* Zambia
* South Africa
So, you can't pinpoint a single location for Swahili. It's a language that spans across a vast geographical area!