In, "The Annals of Platte County.." by Paxton, I only see one reference (through the index) for one Mary Logan who married a John Dunagan,
John Dunagan, born 11 Sept 1814; died 24 Jan 1890. married Mary Logan, daughter of W.A.
1. Clement N. Dunagan, married Eliza Timberlake, daughter of Nic
2. William D. Dunagan, b. 28 Dec 1846; died 4 May 1892. M'd Perd. Pettillo
3. John R. Dunagan
4. Ann Elizabeth Dunagan
5. Melinda Dunagan
Is this the right Mary? There's a tad more (spouses and some children; I'm about asleep :)
My ancestors came from Kentucky to Missouri for the land. I've found them in Boone county before Platte in the 1840 census. The Platte County Historical/Genealogy society is fantastic. I suggest you contact them: http://www.rootsweb.ancestry.com/~mopchgs/
I live close enough that I was able to visit. I contacted them and they had already pulled several probate files.