One tribe — Benjamin was not entirely his, but part of it adhered to Jeroboam, as Bethel, 1 Kings 12:29, and Hephron, 2 Chronicles 13:19, both which were towns of Benjamin.
Related Commentaries of 1 Kings 11:13
1 Kings 11:13
13 Howbeit I will not rend away all the kingdom; but will give one tribe to thy son for David my servant's sake, and for Jerusalem's sake which I have chosen.