Some of the regiments that were filled with recruits from Grimes county were the 2nd, 4th, 8th, 14th Texas Infantry and the 21st Texas Cavalry.

General John B. Magruder established his headquarters at Piedmont in Grimes County and a division of his troops were stationed there. In 1865, soldiers returning from the war broke into a warehouse searching for food and set it on fire. The fire ignited amunition that was stored in the warehouse then spread and burned Navasota to the ground. In 1866-67, a yellow fever and cholera epidemic killed hunreds in Grimes County. Before the war, there were more Negro slaves in Grimes County than there were whites.

Millican in Grimes County was a location where many soldiers surrendered to Federal authorities. A Freedman's Bureau was established at Millican, as well as other locations in the county.