William H. Mumper was the youngest son and the twelfth of 13 children born to Heinrich and Elizabeth Jane (Kiner) Mumper. According to his Civil War pension records, William was born near New Germantown, Toboyne Township, Perry County, Pennsylvania. His pension records also report that William married Sophia (ROTH) Mumper, 18 August 1853 in New Germantown. She was the daughter of Henry and Catherine (Schlauch) Roth and was reportedly born in 1830.

William followed the trade of a blacksmith. On 31 August 1864 he enlisted in Company C. of the 208th Pennyslvania Volunteer Infantry for a period of one year; serving under General John Frederick Hartranft's 1st Brigade, 9th army Corps. He stated that he was 32 years and five months old, and he was described as having a fair complexion, dark hair and gray eyes. He mustered out the following year, receiving $66.67 for his service, less $33.33 for clothing allowance. (He is also noted to have been affiliated with Company K of the 1st Pennsylvania Reserve Infantry.)

On 11 April 1894 William applied for a disability pension claiming rheumatism, inflammation and partial deafness. His application papers provided a wealth of information about his personal life including the birthdates of his nine children. They also show that, during his later years, he was a very ill man.

William was a farmer and blacksmith in Toboyne Township for much of his life, but he moved to Newville, Cumberland County, in the late 1890s where his wife Sophia died 9 August 1899 and where he lived the rest of his life with his disabled daughter, Emma Florence Mumper. William, although ill and totally dependent on his disability pension of $22.50 per month, lived until 25 October 1920. He and Sophia are both buried in the Fogelsanger German Baptist Cemetery in Newburg, Pa.

William and Sophia had the following children: Catherine Elizabeth (29 May 1854); Malinda J. (15 Oct. 1856); James Crawford (30 Oct. 1860); John Russell (29 Aug. 1862); Emma Florence (20 Apr. 1865); George C. (1967-1920); Willis David (1870-1945); Sarah Mae (1872-1933); and Samuel Roth (1875-1920).