Signed diary including printed almanac and eclipse calendar in the opening pages. Mixter writes from various locations. Relates the events of 1861, spending most of his time divided between his home in Hanson, Massachusetts, and his workplace in Boston. Reports political affairs, discussing the secession question with colleagues, and holding a Union meeting. Writes to various governmental officials, including Judge John J. Crittenden, but does not discuss the content of the letters. Reports moving to Boston. Records hearing of the attack on Fort Sumter, South Carolina, 13 April, followed by President Abraham Lincoln's call for 75,000 volunteers 15 April. Reports volunteering for military service 17 April, becoming a member of the 22 Massachusetts Volunteers. Includes various military details, including an inspection by Major McDowell 1 May in Washington D.C., and viewing George Washington's uniform and the Declaration of Independence at the Patent Office. Relates turmoil following the 24 May death of Colonel Elmer E. Ellsworth, the first Union officer killed in the Civil War. Relates a 13 June camp visit by President Abraham Lincoln, Salmon P. Chase, Secretary of the Treasury, and Simon Cameron, Secretary of War. Describes participating in various marches and a battle, followed by a visit home, and reenlistment 7 September. Discusses travel, battle, weather, a visit from his wife, and a review by General George Brinton McClellan. On 15 September, states "Food poor. Bread wormy. Pork all fat. Coffee muddy." On 30 December, records escorting an African American family described as contrabands to the Provost Marshal's office in Washington, D.C. The final pages include an account ledger and company roster. Bound in original leather with a front clasp. Includes a pencil note on the second page indicating that Mixter also served in the 5th Massachusetts Volunteers under Captain David Wardwell.