By the end of the Mexican War, Loomis had served thirty-seven years in the Army and could easily have retired into civilian life as a lieutenant colonel. But he would wear his uniform for another twenty years.
His next stations included Fort Snelling, Minnesota; Fort Leavenworth, Kansas; and Fort Laramie, Wyoming. Here he skirmished with Indians, assisted Christian missionaries, conducted religious services, and buried his wife, Julia, in 1849. Records show they prayed together and ministered to blacks and Indians as lay missionaries.
The Third Seminole War in 1857 found Colonel Loomis making tactical decisions that forced the Seminoles to either surrender or starve. President James Buchanan and others publically praised Loomis for his excellent handling of the Seminoles and closing of the war.
Placed on paid leave from the Army at the end of the war because he had not taken military leave in many years, Loomis hung up his uniform and moved to southern Connecticut with his second wife, Annie. They were very active in supporting their local church and assisting the underground railroad.
Loomis was seventy-two years old when the Civil War began in 1861. Called out from extended paid military leave, he was appointed the senior recruiter for the Union Army by President Abraham Lincoln.
He also became commandant of a Confederate prison camp, where the prisoners viewed Loomis as an elderly man who showed Christian compassion, leading prayer meetings and Bible studies with his chaplain.
When the Civil War ended in 1865, seventy-six-year-old Brigadier General Loomis was the oldest soldier on either side of the war. Two years later, he hung up his uniform for the last time.
He and his wife settled into civilian life and active church ministries in southern Connecticut. He died in 1872 at age eighty-two, a veteran of nearly six decades of military service.
Brigadier General Gustavus Loomis was both a fierce combatant and devout Christian commander. Whether coming from him in his tent, on the field, or in his home, sounds of psalm singing and Scripture reading were common. God was first in his life, then family, and finally career. In all these areas, he was blessed of the Lord.