Pat Magruder has been researching African American descendants in Frederick County, MD, and has found several households, some using the McGruder spelling. She posts her finds on the African American Magruder Descendants Facebook Group, so if you are interested you may want to join that group. Here are her recent posts–
More Mcgruders, Magruders found in Urbana Frederick County , Md. Rueban Mcgruder 1870 census- 25 years old black male. Boarder of Sarah Nailor also black.