The George Martin Trowbridge papers contain a total of 238 letters, 47 of which are written on earlier letters in order to conserve paper. Trowbridge wrote 191 of the letters to his wife, Lesbia ("Lebbie") during his Civil War service with the 19th Michigan Infantry. When his supply of stationery ran low, he reused incoming letters, interlining them with his own writings, and thus 42 letters from Lebbie and 5 from George's friends are also preserved with the collection. The letters span October 9, 1863, to June 22, 1865. Trowbridge apparently intended his wife to preserve these letters for posterity, because he wrote exceptionally detained accounts of the latter part of the Civil War, totaling 1,089 pages of correspondence.
Early letters in the collection describe camp life in McMinnville, Tennessee, which the 19th Michigan occupied for six months from October 1863 to April 1864, with very little to do. Trowbridge was considerably anguished at being separated from his wife, and his long answers to her letters included attempts to govern his household from a distance of several hundred miles. Trowbridge's relationship with his wife emerges with great complexity in their correspondence. George repeatedly discussed the place of women and proper parenting, and he appears to have harbored a nagging suspicion during the first several months of his service that his wife might have been unfaithful to him. His frequent condemnations of adultery, pointed comments concerning infidelity on the part of soldiers' wives, and assertions that he would personally drop a wife who was guilty of infidelity, eventually brought Lebbie to exasperated protests; by the opening of the Atlanta Campaign, references to the subject ceased completely. An evangelical Christian, Trowbridge wrote letters during the occupation period that revealed his interest in the spiritual lives of his fellow soldiers; he described prayer meetings and theological debates. He also frequently criticized the military's secular treatment of the Sabbath, especially in a letter of November 22, 1863.
After the spring of 1864, the unit began its participation in the Atlanta Campaign and in his letters, Trowbridge increasingly discussed military engagements, medical work, duties, and the places and people that the regiment encountered. Of particular note is Trowbridge's 36-page account (November 11-December 17, 1864) of Sherman's March to the Sea, detailing the Union army's destruction of plantations, railroad tracks, and cotton storage facilities. It also provides an excellent description of slavery in Georgia, including working conditions of half-clothed young slaves, the sexual advantage that masters took with their female slaves ("there is white blood in most"), and the illegality of slave literacy. Other topics mentioned include the historical significance of the march, Confederate resistance near Savannah, and the production of "Sherman ties" made by winding heated railroad track pieces around trees. Trowbridge also wrote a 56-page narrative of the March through the Carolinas, dated February 2-March 26, 1865. In this, he gave an account of further destruction of homes, cotton, and infrastructure; of Sherman's reputation as a fighter; of the capture of bank safes in Charleston and Camden; and of the battles of Averasboro and Bentonville.
Toward the end of the war, when stationery got scarce, Trowbridge began writing on letters which Lebbie and others had written to him. Thus over 40 of her letters are preserved. Lebbie's letters, which are still largely legible in spite of the fact that George wrote between the lines of her letters, provide ample family news and many details of life on the homefront. Of particular interest is her description of reactions to Lincoln's assassination in Michigan (on George's letter of May 23, 1865), as well as her discussion of alcohol use by her neighbors (August 28, 1864). Both George and Lebbie comment upon the failed love life of Lebbie's sister, Gertrude A. Fox (b. 1843), who for a time was engaged to her first cousin.