From the Missouri Archives Veterans Database:
Capt Samuel W. Headlee
Co G 72 EMM
enrolled 9 Aug 1862 Springfield MO
ordered into active service 16 Aug 1862 at Sprngfield MO by Gen. Brown
relieved from duty 1 Feb 1863 with remarks: "Absent of this time being a member of the State Legislature:, 38 days"
Capt. Samuel W. Headlee
Co E 16 MO Cav USRC Vols
enlisted 1 Nov 1863 Springfield MO (yes...1863 is what is recorded)
mustered in 17 Feb 1865 Springfield MO
mustered out 1 July 1865 (can't read location)
probably also this man:
Capt Samuel W. Headlee
Co E 6 MO PEM
enrolled and organized 10 Apr 1863 Springfield MO by Maj. C. Sheppard
ordered into active service 10 Apr 1863 Springfield MO by Gen. Holland
Remarks: "M.R. of 3 Aug 1864 does not relieve from duty, nor does it show number of days service rendered. Affidavit of Capt Headlee, attached to roll, states that he entered service 10 Apr 1863 and continued in service 'until the 2nd day of August 1864 when relieved.' Roll is signed by him.
Mustered into US service 24 Aug 1864 from S.O. 166.
I hope this helps.