Based on the 1940 census, your Leo was the grandson of Everett O. Gallup and Maude Selina Ranney...I'm not sure who his parent was. You probably need to get his death record to get that information. However, after that his line is pretty clear...and goes thus.
Robert Merwin Gallup m. Mildred Viola Greene
Peleg Gallup m. Eunice Martin
George Gallup m. Lydia Gallup
George Gallup m. Freelove Packer - Samuel Gallup m. Jemima Enos
George Gallup & Samuel Gallup are both children of:
Nathaniel Gallup & Hannah Gore
Nathaniel Gallup m. Margaret Gallup
John Gallup (III) m. Elizabeth Harris - Benadam Gallup m. Esther Prentice
John Gallup m. Hannah Anna Lake
Your line merges with mine with Nathaniel Gallup and Hannah Gore. To encourage your budding genealogist, you might want to visit Riverside cemetery in Kalamazoo, MI and take pics of their gravestones and upload them to Findagrave.com and then you can see some of the early gravestones online at either Findagrave.com or do a search for Gallup Home and you will get to my webpage at http://freepages.genealogy.rootsweb.com/~gallupfam/
Let us know what you find out!
Home Page: http://carmenj.my100megs.com
Genealogy Page: http://famgen.genheirlooms.com/
Gallup Home: http://freepages.genealogy.rootsweb.com/~gallupfam/
PRA Group 7: http://pragroup7.genheirlooms.com