The Missouri in the Civil War Message Board

William Denison/Dennison

One of these William Dennisons may be a relation of mine. Can anyone help point me to more information so that I can try to determine 1. If William Dennison was in the military, and 2. If he was, which is the correct one? My William Dennison was born in 1839 and was living in St. Francois Co. in 1850, married Susannah Bay in Reynolds Co. in 1857, and was living in Dent Co. in 1860. His parents were James Dennison and Elizabeth Stacy Bell. Susannah Bay Dennison married Jesse Alfred Allison in 1864, indicating that William Dennison had died, probably in the war. (alternate spelling Denison)
The records are for:
William Dennison Co. M, 3rd Mo Cavalry Volunteers who died of pneumonia at Benton Barracks Conv. Hosp. St. Louis, Mo. Jan. 1, 1863- The Third Missouri Cavalry was recruited and organized at Palmyra, Marion County, Missouri. A majority of men came from Illinois so this man can most likely be eliminated.
William Denison, pvt. Co G, 5th Mo Inf Regt. Confederate, who enlisted 1 Jan 1862 and died Feb 1862 at Springfield, Mo. This record states this man was 18 years old at enlistment. The William Dennison born 1839 would have been 23 years old.
William Dennison, Co B. 11th Mo Infantry- mostly men from Illinois, but one company, K, was formed in Franklin County, which is where his wife Susannah Bay was born, although the Bay family lived in Reynolds County by 1850.
William Dennison, Co C., 9th Mo Cavalry same man as below who died 5 Mar 1921- he can be eliminated.
William Dennison, Co C., 10th Mo Cavalry
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It may be helpful to know that
His father James Dennison enlisted in Co. D, 10th Missouri Cavalry and died of disease 26 Jan 1862 at Rolla.
His uncle Moses Harbison Bell enlisted in Co. D, 10th Missouri Cavalry and transferred to Co. K, 2nd Missouri Volunteer Cavalry and survived the war.
His cousin William T or F Bell enlisted in Co. D, 10th Missouri Cavalry and died of disease 16 Feb 1862.
His uncle James Stacy Bell, citizen, died in custody in a military prison in St. Louis, Mo. after Feb. 1865.
Any help is appreciated, especially pointing me toward records that may help my search.
Pamela