Margaret married Owen Shannon in Wilkes County, Georgia on October 12, 1792. Both Owen and his father had served in the American Revolution and received bounty land in Georgia for their service.

In 1822, Margaret and Owen moved to Pecan Point on the Red River, and in 1824 they moved to the area of San Augustine, Texas. In 1827, they settled on a league of land granted to Austin’s second colony by the Mexican Government, and Owen established a trading post, calling it "Montgomery"—his wife’s maiden name. His son, Jacob Shannon, had a league of land five miles west of Owen’s property and already established a trading post that he called "Shannon".

Owen died about 1837. Tradition and some old settlers around Montgomery say Owen was buried on the north bank of Town Creek where his trading post was located. Margaret continued to run the trading post in Montgomery until she became ill and went to stay with her son, Jacob. She died at his home in 1854 and was buried in the Evergreen Cemetery near Dobbin.

Since there was no county, state or national record as to the exact place of burial for Owen, Margaret Montgomery Chapter, NSDAR was granted permission to place a marker to his memory in the "Old Cemetery" in Montgomery, Texas.

In 1959, the Margaret Montgomery Chapter, NSDAR placed a marker on Margaret Montgomery’s grave. The chapter also placed a stone in the Montgomery Cemetery in memory of Owen Shannon and his service in the American Revolution.