Reuben P. Day was in Laclede County, Missouri in Smith Township with his wife Matilda Chasteen/chastain Day, in the 1860 census and 1870. he is listed in Osage Township, Laclede County, MO By 1880 the family is in Sugar Loaf, Arkansas.
Name: Rubin P. Day
Sex: Male
Spouse's Name: Matilda J. Chasteen
Spouse's Sex: Female
Marriage Date: 27 Mar 1857
He enlisted at Springfield, on 27 August, 1864, mustered in on 07 September 1864 and was mustered out on 07 March 1865. Captain Hubbard was over Company B.
The Forty-sixth Missouri Volunteer Infantry was mustered into the United States service in September, 1864, served the term of six months, and was mustered out at Springfield May 24, 1865. A colonel's commission was issued to Robert W. Fyan September 17, 1864. On the same date Thomas A. Reed was commissioned lieutenant-colonel. On December 1 Thomas K. Paul was commissioned major. Adjutant Mack, Quartermaster James Owen and Surgeon Roesch were the other field officers. Company A was commanded by R.J. McElhany, Company B by J.T. Hubbard, Company C by E.D. Brown, Company D by William B. Allen, Company E by J.P. Julian, Company F by D.C. Rug, Company G by William Brixey, Company H by Moses L. Alsup; Company I by William J. Pyland and Company K by Henry Sullivan.
http://genealogytrails.com/mo/webster/history_chapter3.html

It appears Reuben P. Day served as a sgt from March 8 1865-,October 26 1865 in the 14th cav company H under Capt. Robertson. He mustered out at Ft. Leavenworth, KS.
According to findagrave Reuben P. Day was born in 1825, Campbell County, Tennessee and died 7 May 1893 (aged 67–68) 7 May 1893 (aged 67–68)
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