There are three geographical regions designated within a state, one in the north of the state, one in the centre of the state and one in the south of the state. What is the correct way to describe the regions?:
1. North Region, Central Region and South Region or
2. Northern Region, Central Region and Southern Region

The quick answer is there is no answer. You can choose either. If it forms part of a name, you must use that version, otherwise you can do what you like.