2 and 3 are correct. Just double check your spelling. It should be "northern."

Number 3 is correct. My hometown is in the northern part of China.

3 is ok (if you correct the typo in northern) but not 1 or 2. However, the most natural-sounding options (at least to me - I'm from the UK) would be "I'm from northern China" or "I'm from the north of China".