Onn or ONN may refer to:
- Onn, the Irish name of the seventeenth letter of the Ogham alphabet
- Optical neural network
- Onion News Network
- ONN (radio), the Ohio News Network
- Onn., a consumer electronics brand that is a store brand for Walmart
- Onn Abu Bakar, a Malaysian politician
- Onn Jaafar, a Malayan politician
- Onn Hafiz Ghazi, a Malaysian politician
- Melanie Onn, a British politician
- Shmuel Onn, a mathematician