Karetu is a locality in the Northland Region of the North Island of New Zealand. Kawakawa is to the west, and Waikare is northeast. The Karetu River flows from the Russell Forest in the southeast through Karetu, and joins the Kawakawa River shortly before it flows into the Bay of Islands.
The name is a Māori word for Hierochloe redolens, a sweet-scented grass used in sachets and to make girdles.
Karetu School is a decile 3 coeducational primary school serving years 1-8. It has a roll of 52.; the school was established in 1886.