Served for the Confederacy during the Civil War. He married Jennie Colombe.

Frank Mullen, 24, married Jennie Colombe, 19, on 26 Apr 1881 at the home of Mr. Jno B. Colombe on the Missouri River. Record shows the residence of Frank to be San Antonio, TX and Jennie to be Rosebud, DT. Parents are Ralph and Bertha Mullen of San Antonio, TX and Jno. B. and Josephine Colombe. Marriage performed by Wm. J. Cleveland. Witnesses: Jno. B. Colombe, Levi Trudell and Mrs. Levi Trudell. (Source: Rosebud Mission Church Records, Book A, #007856517, Image 151)

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Bio from "History of South Dakota" by Doane Robinson, Vol. I (1904), pp 700-701.

FRANK MULLEN is one of the honored pioneers of South Dakota, where he has maintained his home for more than thirty years while for more than two decades he has held the responsible office of clerk of the Rosebud Indian agency, with headquarters in the village of Rosebud, Meyer county. He is held in high esteem by all who know him, is a typical westerner in spirit and is well deserving of representation in this historical compilation. 

Mr. Mullen is a native of the great Lone Star, state of the Union, having been born in Bexar county, Texas, on the 6th of July, 1848, and being a son of Ralph and Caroline (Black) Mullen, natives respectively of North Carolina and Virginia and both of staunch Irish lineage. They were numbered among the early settlers in Texas, where they passed the closing years of their lives, the father having there devoted his attention to the vocation of law. The subject of this sketch received his educational training in the schools of Austin, Texas, and in 1863, when but fifteen years of age, he was appointed to a clerkship in the quartermaster's department of the Confederate army, the Civil war being in progress at the time. During 1864-5 he served as captain and assistant quartermaster of the Confederacy in his native state, and after the close of the war he became clerk in the same department of the Union service, thus serving in Texas from 1866 to 1869, inclusive. In 1870 he engaged in business in the city of San Antonio, that state, continuing operations there until 1872, when he came as a pioneer to the great undivided territory of Dakota, where he was in the employ of the Northern Pacific Railroad Company until 1874, when he took up his residence at the old Spotted Tail Indian agency, with whose affairs he became identified. On the 23d of August, 1883, he was appointed clerk at this agency, whose name had been changed to Rosebud its present cognomen. and he has since remained incumbent of this office, in which he has given most discriminating and acceptable service. In politics he gives an unqualified allegiance to the Republican party, and fraternally, he is one of the prominent Masons of the state, having passed the degrees of the lodge, chapter and commandery in the York Rite and attained the thirty-second degree and been proclaimed a Sublime Prince of the Royal Secret in the consistory of the Ancient and Accepted Scottish Rite at Aberdeen, while he is also affiliated with the Ancient Arabic Order of the Nobles of the Mystic Shrine, the Benevolent and Protective Order of Elks and the Independent Order of Odd Fellows. Both he and his wife are communicants of the Protestant Episcopal church. 

On the 25th of July, 1880, was solemnized the marriage of Mr. Mullen to Miss Jennie Colomb, who was born on the 16th of December, 1859, being a daughter of John B. and Josephine (Dorion) Colomb. They are the parents of three children, Amy, Norah and John.