The Kizimkazi Mosque is a mosque situated on the southern tip of the island of Zanzibar in Tanzania and is one of the oldest Islamic buildings on the East African coast.Despite its name, it is located in Dimbani, not Kizimkazi, which is three miles away (this is because the official names of these two joined villages are Kizimkazi Dimbani and Kizimkazi Mtendeni). According to a preserved kufic inscription, it was built in 1107 by settlers from Shiraz. Although the inscription and certain coral-carved decorative elements date from the period of construction, the majority of the present structure was rebuilt in the 18th century.

It's located by the heart of Dimani a few steps from the beach. I think archives department should provide more & specific informations bout the whole history of the oldest mosque (I think by the location).