Just over one month after the discharge of the 124th, General Lee again attempted to invade the Union States, this time making it to Pennsylvania. Governor Curtin declared another state of emergency, and Clayton and most of the members of the 124th were hastily assembled into the newly formed 29th Emergency Regiment, Pennsylvania Volunteer Militia. The new 29th remained in Chester and Delaware counties during the Battle of Gettysburg, but, after the battle, Colonel Hawley led a brigade consisting of the 29th and two New York regiments in pursuit of the defeated Confederate troops. This ended Clayton's active involvement in the Civil War. After his service, he took a position as a teacher of military tactics and other subjects at the Village Green Seminary in Delaware County, Pennsylvania.