The records in his CMSR end on May 20, 1864 as follows:
Captain Thomas Irby " appears on a roster of the officers of the organization named above. Roster dated May 20, 1864. When elected or appointed - April 5, 1864. " (He was promoted to Captain on April 5, 1864 after holding the rank of Private and then 1st Lieutenant.)
There are no other records in his CMSR after May 20, 1864.
Some other information from his CMSR:
He enlisted August 12, 1863 in Chickasaw County, Mississippi and was age 39 years at the time. He resided in Chickasaw County, Mississippi and was born in Laurens County, South Carolina. His occupation was a farmer.
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He appears on the 1860 census:
Name: Thomas Irby
Age in 1860: 35
Birth Year: abt 1825
Birthplace: South Carolina
Home in 1860: Division 1, Chickasaw, Mississippi
Gender: Male
Post Office: Chickasaw Mills
Household Members:
Name Age
Thomas Irby 35
Louisa Irby 22
George Irby 3
William Irby 2
Source Citation: Year: 1860; Census Place: Division 1, Chickasaw, Mississippi; Roll: M653_579; Page: 108; Image: 112; Family History Library Film: 803579.
Source Information: Ancestry.com. 1860 United States Federal Census [database on-line]. Provo, UT, USA: Ancestry.com Operations, Inc., 2009. Images reproduced by FamilySearch.
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There is another researcher who claims that Thomas Lockhart Irby died Jul 7, 1864 in the Civil War and that his widow, Louisa Georgia Walden, then married George W. Owens.
Refer to the following links:
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George W. Owens and Louisa Georgia Walden appear on the 1870 census and the 1880 census as follows:
Name: George W Owen
Birth Year: abt 1844
Age in 1870: 26
Birthplace: Tennessee
Home in 1870: Northern Division Subdivision 2, Chickasaw, Mississippi
Race: White
Gender: Male
Post Office: Houlka
Household Members:
Name Age
George W Owen 26
Louisa G Isby 32
George H Isby 14
Wm S Isby 12
Cora Isby 10
Thos J Isby 7
Source Citation: Year: 1870; Census Place: Northern Division Subdivision 2, Chickasaw, Mississippi; Roll: M593_724; Page: 45A; Image: 93; Family History Library Film: 552223.
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Name: George W. Owens
Home in 1880: Calhoun, Prairie, Arkansas
Age: 35
Estimated birth year: abt 1845
Birthplace: Tennessee
Relation to Head of Household: Self (Head)
Spouse's name: Louisa G. Owens
Father's name: James Owens
Father's birthplace: Ohio
Mother's birthplace: Pennsylvania
Occupation: Farmer
Marital Status: Married
Race: White
Gender: Male
Household Members:
Name Age
George W. Owens 35
Louisa G. Owens 42
James Owens 71
Cora I. Irby 19
Thos. Joseph Irby 17
James A. Owens 14
Thos. J. Owens 12
Andrew A. Owens 5
Orville H. Owens 3
Isaac Branch 27
Source Citation: Year: 1880; Census Place: Calhoun, Prairie, Arkansas; Roll: 54; Family History Film: 1254054; Page: 238C; Enumeration District: 250; Image: 0595.
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Regards----