I am not related to this family, but I have a booklet with a little information on someone with a similar name. The booklet is 'Crossroads and Corners' by Eugene Scheel, and is about Prince William Co., VA.
"Whitmer - here where the roads to Buckhall and Bland's Ford split, lived C. Franklin 'Frank' Whitmer and (first wife)Beulah, and (second wife) Emma Cornwell Whitmer. Frank and his brother, Gilbert Whitmer, built the still-standing house at the turn of the century. Frank farmed and also operated a cider mill, taking as payment the juice. Frank and Emma died in the late thirties with the farm passing to son, Guy Whitmer. He was a Manassas accountant who, with his wife, the former Alice Shortt, lived here until the mid-sixties. Frank's father, Swiss-born Suffary Whitmer, helped organize the Manassas Lutheran Church and donated land for the Lutheran Graveyard, on a knoll just east of Whitmer."
Sources were Ann Beulah Whitmer Crawford and Alice Shortt Whitmer.