"In Company F, 2d Michigan, there enlisted at Flint [MI] Franklin Thompson (or Frank, as usually called), aged twenty, ascertained afterward and about the time he left the regiment to have been a female, and a good looking one at that. She succeeded in concealing her sex most admirably, serving in various campaigns and battles of the regiment as a soldier; often employed as a spay, going within the enemy's lines, sometimes absent for weeks, and is said to have furnished much valuable information. She remained with the regiment until April, 1863, when it is supposed she apprehended a disclosure of her sex and deserted at Lebanon, Kentucky, but where she went remains a mystery."
So reads the Michigan Adjutant General's report, published as revised in 1882. In May of that year, Sarah Emma Edmonson Seelye wrote the AG asking for a certificate of service in order to pursue a pension from the US Government. Paper in hand, she approached the Congress and, on July 5, 1884, a private bill awarding her the pension was signed into law. In July 1886, a bill removing the charge of desertion from her record also became law.
The Michigan historical marker erected in 1992 in Flint includes this: "The Second Michigan saw action at the first Battle of Bull Run and, as part of the Army of the Potomac, at the Second Bull Run and Fredericksburg. Thompson performed all of the duties of a soldier including nurse and mailcarrier. In 1863 he became ill, but was denied a furlough. To preserve his identity, he deserted."
"The Mysterious Private Thompson" by Laura Leedy Gansler handles the story well, suggesting the spy aspect is likely fiction. But completely genuine was the warmth with which she was greeted at the October 1884 regimental reunion in Flint.
She was one of Michigan's own.