For black Magruders, McGruders, McCruters (and other name variants) there are three likely origins of the name: a blood relationship to white Magruders; adopting the name after gaining freedom; or acquiring the name early, perhaps in the 17th or 18th century, and carrying it from then on, no matter where descendants ended up.
You can learn more about how families selected their names after Emancipation on the Changing Names page of Facing History and Ourselves.
All Magruder/McGruder roots eventually lead back to Maryland. Your ancestors came from there, or carried the name from there, or the white family they got their name from came from there. I’ll soon have a page on researching black ancestors in Maryland.
If you are looking for ancestors I have two recommendations—
Join the two Facebook groups, African American Magruder/McGruders & Magruder/McGruder Family Genealogy, where you can connect with people searching for ancestors in multiple states and counties. Read through old posts to see if anyone might be related to you or searching in the same locale, and post your own questions. You’ll find a warm and helpful community of fellow searchers. Both groups are administered by Jill Magruder Gatwood, an outstanding resource for any black Magruder/McGruder building a family tree or working with DNA. She may be able to help you access DNA testing.
Start reading Robyn Smith’s Reclaiming Kin genealogy teaching blog. Not only is Robyn a brilliant and deeply knowledgeable researcher of black genealogy, she’s a Maryland specialist. Be patient with yourself: she has been doing this for decades, you may just be starting. Start reading and learning with Start Here and Resources for Researching Slavery. Robyn also offers inexpensive webinars on various research methods and topics. If you’re not available at the scheduled time, all registered participants get a link to watch the webinar for 30 days. I take screenshots while watching and later rename and organize them to accompany my notes. Robyn also sells genealogy forms to help you organize specific categories of information.
More info on this site: Research Tips: Getting Started / Researching Black Ancestors in Maryland / The Alabama Black McGruders / Af-Am Magruders in Washington DC Slavery Petitions, 1862 / Af-Am Magruders in P.G. County MD Slave Statistics, 1867 / Af-Am Magruders in Montgomery County Slave Statistics, 1867 / Washington McGruder /
To find people enslaved by a few Magruder families in Maryland, see the pages under Slavery’s Legacy. I hope to add more to these pages in future.
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Not all black Magruders and McGruders are related to the Alabama Black McGruders featured on ABC’s Soul of a Nation. That family’s roots have been traced to Charles McGruder, Sr., and to his parents, Ned and Mariah Magruder, who were born in Georgia on the plantation of Ninian Offutt Magruder. Ninian migrated to Georgia in the early 1780s, along with his first cousin Ninian Beall Magruder. In Columbia County they joined an already established community of Magruders and related families, including the surname Drane, and all these families intermarried extensively. Ned Magruder (b. abt 1795) was the son of Ninian and an unknown enslaved woman. (When The Alabama Black McGruders book comes out, you can read speculations about who Ned’s mother might have been.) Ned and Mariah, along with their children, were taken to Alabama by Ninian’s youngest daughter, Eleanor Magruder Wynne. One of Eleanor’s brothers, Zadock, also settled in Alabama, in Macon County; to my knowledge, the enslaved people he took with him have not been researched.
If your family goes back to either Georgia or Alabama, you might find DNA matches among the Alabama Black McGruder family. If you think you are directly related to them, post on one of the Facebook groups and one of the family members or researchers there will help you figure out the family tree.
If you get a DNA match, but are not descended from the Alabama family directly, there are at least two places you can start looking. If your family is from Macon County, your people may have come from the plantations of William Reardon Magruder, son of Zadock Magruder, who was Ninian’s son and Eleanor’s brother. If that doesn’t sound like your locale, you can start searching records pertaining to the slaveholding Magruder, Drane, and related families in Georgia. If you have traced your family back to, or close to, Emancipation, and/or you know where they were living, I might be able to help you identify some families to start searching. Georgia and Alabama records are relatively easy to use on FamilySearch.org (better than MD records). Some of the Georgia Dranes and Magruders also migrated west into Mississippi, Kentucky, and elsewhere.
For information on the Alabama DNA project, contact Jill Magruder Gatwood by posting on one of the Facebook groups—African American Magruder/McGruders or Magruder/McGruder Family Genealogy. I cannot help you with the DNA project; if you write to me I will simply forward your message to Jill. I am happy to do this if you can’t use Facebook, though I urge you take the plunge and join these two marvelous groups.
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Magruder's Landing 
I am looking for info on Af Am Magruders from Hampshire co. Va. later WV… My great grandmother was Eliza Catherine Magruder… born in 1869. Her father is believed to have been white.. his name was Caleb Magruder. She had many siblings… one was a brother Harry Magruder. Her home was near Romney, WV… any information would be greatly appreciated. Thank you.
I am from Hezekiah Magruder and just joined both the African American and Macgruder Facebook pages. I checked my DNA matches and sent emails to some of my 4-6 cousins. I also discovered through archives.com that we are somehow descended from John Billington who came over on the Mayflower through his son Francis and his granddaughter Mary. I can only assume they were the slave holders of Hezekiah who produced my four times great grandmother Margaret Goe. On a sheet I printed, it also links Abraham Lincoln to my line as my 5th cousin 2 x removed. I find that astounding as no where else have I found any of that information or the Mayflower connection. I look forward to finding out more about these people as it amazes me that I can be both of European (slaveholder) and African (slave) folks. I watch Finding Your Roots faithfully and even corresponded with Henry Louis Gates, Jr. To give him this info. I got a response back and he seemed thrilled I had been able to go back this far. The last episode I remember him being thrilled that the slave ancestors of Epatha had names and in my Hezekiah line, the names are clearly listed. I have been doing my family genealogy for over 30 years and these recent discoveries have my mind blown, to say the least.