I have not actually seen anything that gives his name as “Thomas F. M. Campbell”, but the marriage license very clearly says Thomas F. Campbell, and the 1900 census very clearly says Thomas M. Campbell. Since during the 1800’s “F. M.” was very common as a pair of given name initials (for Francis Marion), that is the most likely explanation for seeing both variants.

1880 census of Knox Co., Missouri, Edina township, lists Thomas F. Campbell, age 26, b. Ohio Ireland Ohio, farmer, living as a boarder with the widowed Rosa A. Reid, age 57, and her children.

Her death certificate records Lulu M. Campbell, age 52 years 7 months 27 days, born 10 June 1862 in Clinton Co., Ohio, died 6 Feb 1915 in Edina, Knox Co., Missouri, widowed, father John Mathew, mother’s maiden name Mary E. Miller, both born in Clinton Co., Ohio, cause of death pulmonary tuberculosis, informant L. F. Ootty (sp?), Edina, Mo, burial in Catholic Cemetery.

The 1900 census gives her birthdate as June 1864. I cannot find a good fit in the 1870 or 1880 census, in either Ohio or Missouri, so I don’t know which year of birth is more likely to be correct.

Knox Co., Missouri marriage books record the marriage of Thomas F. Campbell, over 21, and Miss Lulu Mathews, over 18, both of Edina, Knox Co., Mo, at St. Joseph Church, by John Fitzgerald, pastor of said church.

1900 census of Knox Co., Missouri, Center township, Edina ward 3, enumerated 12 June, lists on p. 16A as family #339/358:
Campbell, Thomas M., 46, b. Jan 1854, Ohio Ohio Ohio, assessor; Lulu M., wife, b. June 1864, married 17 years, mother of 6 children, 1 living; Elsie M., dau, 14, b. Jan 1864, Mo Ohio Ohio.

1910 census of Knox Co., Missouri, Edina ward 3, enumerated 30 April, lists on p. 12B as family #278/286:
Campbell, Lulu M., 46, b. Ohio Ohio Ohio, widowed, mother of 6 children, 1 living, own income; Elsie M., dau, 23, single, b. Mo Ohio Ohio.