At the Fort Hood Sentinel, Robert Miele has an article noting veteran Cathy Williams which includes:
She was the only woman to serve in the United States 
Regular Army as a Buffalo Soldier. She served for three years at a time 
when women were prohibited from serving in the U.S. military, and she is
 the only documented woman known to have served during this period.
In 1844, Williams was born a slave in Independence, Missouri. 
Her mother was also a slave, but her father was free. In 1848, Williams 
and her mother were sold to the Johnson Plantation to work as house 
servants. Williams never saw her father again.
In the fall of 1861, Union Soldiers rode into the Johnson 
Plantation and freed all of the slaves. Williams and her mother left for
 Jefferson City, Mo. During this time, freed slaves were treated as 
contraband of war, so Williams and her mother were separated and forced 
to serve Union units. Unfortunately, Williams would never see her mother
 again either.
Williams was 17 years old at the time she was assigned to do 
laundry for the officers of the Eighth Indiana Volunteer Infantry. For 
3.5 years, she walked alongside the infantry Soldiers, as they marched 
hundreds of miles across the South. 
When the Civil War ended in 1865, Williams returned to Missouri 
in search of her mother. She met her cousin who told her he was going to
 join the Army and earn $13 per month. Williams decided she wanted to 
join, also. She cut her hair short and donned men’s clothing. She 
enlisted into the United States Regular Army as a male Soldier on Nov. 
15, 1866, in St. Louis, Mo., under the name Pvt. William Cathay.   
veterans