Although the headstone (pictured on Find a grave) clearly identifies him as having served in company E of the 91st Pennsylvania, I doubt that he served in the 91st; the regiment was not in Camp Curtin in 1862, and I do not understand why he would have been there. Further, the National Archives was unable to find a compiled service record for him. However, since the regimental records from 1862 were lost, it is possible, though unlikely, that he was detached there and no record remains.
Note that his headstone, like the others in the cemetery, were replaced in 2012 because they were nearly illegible; the Veterans Administration did verify their service before providing the headstones. [source: 4]
He (allegedly) served as a sergeant, in company E or B. [sources: 1 (E), 2 (E), 3 (B)]
He died at Camp Curtin, Harrisburg, Dauphin County, Pennsylvania. He died of catarrh. On 5 August 1862, he was buried, in Harrisburg Cemetery, Harrisburg, Dauphin County, Pennsylvania. [sources: 1, 2, 3 (died 6 Aug 62)]
1 Camp Curtin Post Hospital, section Z, Harrisburg cemetery (Alonzo Page)
2 Find a grave, memorial 101059585, created by Donald Coho, added 21 November 2012, accessed 2 November 2013 (Alonzo Page)
3 US registers of deaths of volunteers, 1861-1865, National Archives and Records Administration, record group 94 (Alonzo Page)
4 'Boy Scout takes on massive job of replacing Civil War headstones in Harrisburg Cemetery', on PennLive, by Allison Dougherty, 4 July 2012, updated 5 July 2012, accessed 2 November 2013 (Alonzo Page)