Is Ceres in the inner solar system or outer solar system? Do we consider the dwarf planet Ceres to be in the inner solar system or outer solar system (or possibly neither / in between).  It is located within the asteroid belt, but is the asteroid belt part of the inner or outer solar system?
Inner. The entire asteroid belt is in the Inner Solar System (now). The definition of "Inner" vs. "Outer" is non-arbitrary, based on the current "frost line", approx. 5 a.u. radius.

https://en.wikipedia.org/wiki/Frost_line_%28astrophysics%29

https://en.wikipedia.org/wiki/Solar_System#Inner_Solar_System