Hamlin had four sons who grew to adulthood: Charles Hamlin, Cyrus Hamlin, Hannibal Emery and Frank Hamlin. Charles and Cyrus served in the Union forces during the Civil War, both becoming generals, Charles by brevet. Cyrus was among the first Union officers to argue for the enlistment of black troops, and himself commanded a brigade of freedmen in the Mississippi River campaign. Charles and sister Sarah were present at Ford's Theater the night of Lincoln's assassination. Hannibal Emery Hamlin was Maine Attorney General from 1905 to 1908. Hannibal Hamlin's great-granddaughter Sally Hamlin was a child actor who made many spoken word recordings for the Victor Talking Machine Company in the early years of the 20th century.