My ancestor served in the 24th Regiment Missouri volunteers-company C. His name was William A. C. Thompson

He was discharged on Jan 12, 1863 from Van Buren. According to his discharge papers he was stationed in Patterson, MO on Dec 3, 1862 and had been unfit for duty 60 days.

My questions are:
1. Was there a fort in Van Buren? Why would he be transported from Patterson to Van Buren?
2. Is it true that Captain Martindale was the commanding officer of this company? I've looked and found various answers.

Thank you,
William