Tracking down "Dessie" McKee's husband would not have been too much trouble, I'd thought, given that his name was given as "William Black" in "The Family Lineage of the Butler County McKees" (1922, by James A. McKee and Anna McKee Halsey). With a couple of locations, no less (Piqua, Ohio about 1900 and Detroit, Michigan about 1920). However, given the head-of-household indexes available prior to 2004 for the 1900-1920 census, I could find no trace of a family for any William Black with a wife named Decima (or variants).
While poking around for some Showalter data (Dessie's older sister Ella married Joseph Baltzell Showalter), I happened across several pages at Ancestry.com that broke the wall down. Ancestry World Tree sites for the 'Dodd-Munoz Family' and 'Leggett of Ely, Cambridgeshire, England and West Farms (Bronx), New York' both contained Showalter and McKee family I had not seen before. The Dodd page, in particular, had a transcript of the biography of David McKee, Decima's father, that mentioned that Decima was the wife of 'J. T. Black' of Piqua, Ohio. Further reading showed that the 'J' stood for 'James'. Well THAT certainly helps, having the correct first name. Google searches on variant orders of terms "rev james t black" yielded few hits, but they were golden. An interesting one at a Delaware County, New York history site (www.dcnyhistory.org/bf1b.html) had entries from 'Early Bovina Families and their Descendants' showing children of Rev. James Black and Decima McKee. One of these children, William Thomson Black, had a uncle of the same name (Rev. James's brother) who had a biography in the 1895 'Biographical Review' (also at the dcnyhistory.org site). In this bio, James is mentioned as a 'Presbyterian clergyman in Boston, Mass.'
Sure enough, that is where I was finally able to locate Rev. James and Decima Black's family in the 1900 census, in Boston. And knowing that James and William had been born in Grant County, Wisconsin, made it much easier to narrow down the list of James Black's to look through. I then found 'James D.' and Decima Black in the 1910 Detroit census, as anticipated.
The moral of the story is: it sure pays to know WHO you're looking for, even when you think you know where to look.