I am trying to fill in some missing years and people in the life of John Denton Martin, my wife's paternal grandfather.

Based on varying degrees of documentary evidence, we know the following:
John was born 25 July 1853 in Franklin, Johnson County, Indiana, son of Dr. James O. Martin and Charity Denton. James O. Martin is descended from Samuel Martin of Dunbar, Fayette Co., Pennsylvania.

John appears with the family in the 1860 and 1870 census. In the decade leading up to the 1880 census, John has apparently been married, fathered a daughter and been divorced. He appears in the 1880 census in Franklin described as divorced and living with his widowed mother, Charity, and Charity's granddaughter, Leola S. Martin, age 4. Since records indicate that of Charity's 3 children, one daughter died young, another daughter is already married with children by 1871, Leola is presumed to be John's daughter.

Brickwall #1: To whom was John married and divorced from by 1880?
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John is described in "History of Johnson County, Indiana' by D.D. Banta in 1888 as "now living in the west." We lose sight of John D. until 1891 when he is listed in the Mobile, Alabama City Directory as a clerk at the Battle House Hotel. Listed as a bellman at the same hotel is his sister's son, Ashley Voris. On 30 April 1893 he is listed on the birth certificate of a son, John D. Martin, in Burlington, Iowa along with his wife, Winifred Delaney. However, he is not listed in the Burlington City Directories for 1890 thru 1893. A second son, Merlin, is born 22 May 1894 in Mobile, Alabama.

By 1900 the family -- John D., Winifred, John D. Jr., Merlin and another son Joseph -- is running a hotel in Washington, Wilkes Co., Georgia. There is no sign of Leola in this first surviving census since her appearance in 1880.

Brickwall #2: What happened to Leola?
Brickwall #3: When and where did John and Winifred marry.

By November 1904, the family is in Bronx, NY where they remain for at least the next 25 years.