Diary, 1870, of Samuel K. Thompson, 2nd Lieutenant of the 25th Regiment of the U.S. Infantry, which was one of the all African-American regiments founded in 1866 that are also referred to as "Buffalo Soldiers." Thompson was a white commanding officer of the regiment.

The diary starts out in early 1870 in New Orleans, Louisiana, where the regiment had its headquarters. Thompson then describes marching to Ft. Davis, Texas. His entries are regular and often detailed and give a good impression of day-to-day occurrences. An entry inside the front cover gives directions on where to send the diary in case of his death, with special instructions in case it should be found by a Mason like himself.

The back of the diary has a few personal accounts and several pages of detailed listings of letters written and received.

Included in the back pocket of the diary are several loose items: an undated photograph of Thompson in uniform (dedicated to his sister Lizzie, who died in 1866), several notes and receipts, an obituary for a colonel of his regiment, a General Service Code Card, and a short letter written to Thompson by his wife Alice in 1876. Also contains a threatening note from the Ku Klux Klan: "Beware! the Ku Klux Klan. Warning 1st." with a drawing of a skull and crossbones, knife, and coffin.