Tilapia are native to Africa. They're members of the cichlid family of fish, which has branches in both South America and Africa. However, the three genera which are raised for aquaculture -- Oreochromis, Sarotherodon and Tilapia -- are African in origin.
The oldest tilapia species farmed for aquaculture is the Nile tilapia, or Oreochromis niloticus. It was farmed by the ancient Egyptians and is native to the Nile river. Most of the tilapia farmed commercially outside of Africa are the Nile tilapia or belong to the same genus. Sarotherodon melanotheron, the blackchin tilapia, is native to West Africa. It isn't farmed, but it is captured by fishermen in the wild. The genus Tilapia is derived from East African lakes.