Captain John M. Grandberry of Harris County, Georgia and John Grandberry of St. Landry Parish, Louisiana are 2 different individuals as shown by the 1860 census records below.
Apparently, John Grandberry of St. Landry Parish has been confused with Captain John M. Grandberry of Georgia.
If John Grandberry of St. Landry Parish was indeed a Confederate soldier, there is no formal military record of him that still exists.
The census records follow:
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John Grandbary--age 25--born St. Landry Parish
Julie Prevot--age 20--born St. Landry Parish
Source Citation: Year: 1860; Census Place: Opelousas, St Landry, Louisiana; Roll: M653_424; Page: 0; Image: 251.
Source Information:
Ancestry.com. 1860 United States Federal Census [database on-line]. Provo, UT, USA: The Generations Network, Inc., 2004.
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Mary B Grandberry--age 48
John M Grandberry--age 26--born Georgia--(Captain John M. Grandberry)
Geo A Grandberry--20
M K Grandberry--18
Eugene Grandberry--16
Mary B Grandberry--13
Robert Grandberry--10
Lucion Grandberry--6
Source Citation: Year: 1860; Census Place: Georgia Militia District 696, Harris, Georgia; Roll: M653_126; Page: 528; Image: 529.
Source Information:
Ancestry.com. 1860 United States Federal Census [database on-line]. Provo, UT, USA: The Generations Network, Inc., 2004.
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There is also a marriage record of John and Julie Grandberry of St. Landry:
Name: John Grandberry
Spouse: Julie Prevost
Marriage Date: 17 Nov 1859
Marriage Place: St. Landry
Source: Louisiana Marriages 1718-1925 [database on-line]. Provo, UT, USA: The Generations Network, Inc., 2004.
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John Grandberry of St. Landry Parish also appears on the 1850 census living with his stepfather Marcel Richard and his mother Julie Anne Meche:
Marcel Richard--42
Julienne Richard--36
Marcelite Richard--7
Victor Richard--4
John Berry--age 13
Source Citation: Year: 1850; Census Place: , St Landry, Louisiana; Roll: M432_240; Page: 28; Image: 56.
Source Information:
Ancestry.com. 1850 United States Federal Census [database on-line].
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The only Grandberry from Louisiana with a military service record is Private Jesse D. Granberry who served in the Madison Light Artillery, Captain Moody's Company.
Best regards to all--