Amos Fithian Garrison I was born around 1808 in New Jersey to William and Ruth Garrison. He was baptized in Deerfield, New Jersey, on March 10, 1809. His father died on May 3, 1819, and his mother died four years later.
He moved to Missouri around 1837 and earned a living as a government surveyor. He served as a lieutenant in the Second Seminole War. In June 1846, he received a commission as captain in the Commissary Department, and he served until November 30, 1848. Garrison settled in Fort Osage, Missouri, after leaving the army. He married a woman named Armilda, and they apparently had no children. He worked as a farmer, and by 1850, he owned $11,000 of real estate. He also enslaved at least eleven people. By 1860, he owned $6,000 of real estate and $6,600 of personal property, including at least six enslaved laborers.
He returned to the United States army on August 7, 1861, receiving a captain in the Commissary Department. He was stationed in the New Mexico Territory. In December 1862, territorial officials praised his “untiring energy as an officer, his unswerving loyalty to the Government, [and] his unceasing efforts in the discharge of his duties as disbursing agent of the Government.” He mustered out on January 10, 1866, and he later received a brevet promotion to major.
After the Civil War, he served as vice consul at Guaymas, Mexico. He died in Hermosilla, Mexico, on August 5, 1877.