Chief Keef -- Out Of Rehab and Chicago ... Hello, California!!

Chief Keef is out of rehab and knows exactly what he needs to get his life back on track ... some high-grade California sunshine.

Keef's attorney tells TMZ, Chief completed his rehab stint in Orange County, CA -- where he was working on his weed addiction -- and immediately flew back to Chicago to visit his daughter, but he's not staying long.

We're told Keef is planning to move to L.A. ... where he can work on new music in his recording studio. The last thing holding him back in Chi-town is a progress hearing in court Feb. 28.