The 138th Pennsylvania Volunteer Infantry Regiment was formed at Camp Curtin, located in Harrisburg, in August of 1862. the formation of the unit was the response to President Abraham Lincoln's call for 300,000 troops in 1862. The first troops arrived on the 16th and by the 26th formation was completed. Men in the regiment originated from Montgomery, Adams, Bucks, and Bedford counties. Originally, each man was called to serve for nine months service however, an order latter extended the time to three years. Charles K.L. Sunwalt, a resident of Adams County, was made commanding colonel. Under his command the regiment moved to Baltimore, Maryland.