Isaac W. Patton was born in Fredericksburg, Virginia, the descendant of one of the first colonial families. His grandfather was Revolutionary War general Hugh Mercer, and his father was John Patton, a prominent lawyer and politician in the Richmond area. He was educated at the Fairfax Institute and then began studying law under his father at the age of nineteen. When the Mexican American War broke out, he put aside his studies and joined the Army. He was commissioned as a Second Lieutenant in the Tenth United States Infantry. By the end of the war in 1849, he was a Second Lieutenant in the Third Artillery and stationed in California. He served there until he resigned from the military in 1855 and returned to Virginia. That same year, he married Frances E. Merritt, the daughter of a doctor in Richmond. Two years after their marriage, the couple moved to St. Bernard Parish, Louisiana in order to manage a cotton plantation.
