I could find nothing of Maxey's unit. I would suspect it was a short term outfit organized for local defense probably to meet a possible threat.

J. C. Bruce, Private, Captain William P. Maxey’s Company of Mounted Infantry, Mississippi State Troops, for local defenses, enlisted April 26, 1863 at Brandon, no other records

Note, only one muster roll for Maxey's company is found in the records, that for April 27, 1863, neither place nor presence of Pvt. Bruce is stated

M269: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Mississippi