It's rather interesting finding two prominent citizens by the same name, born in the same year. See the 1860 Federal census enumerations below:
Young D. Harrington, age 44, 1st Lieutenant, Captain Isaac Dansby's Company, Ochiltree's Regiment Volunteers**, enlisted April 21, 1862, joined for duty and enrolled May 3, 1862 in Rusk County, Texas by W. B. Ochiltree for 3 years, detached Sept/Oct. 1862 as Assistant Surgeon, left sick at Camp Nelson, Arkansas November, 1862, tendered resignation November 20, 1862 "upon grounds of bad health," resigned December 5, 1862
** This company subsequently became Company G, 18th Regiment Texas Infantry
M323: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Texas
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1860 United States Federal Census about Y D Harrington
Name: Y D Harrington
Age in 1860: 42
Birth Year: abt 1818
Birthplace: Georgia
Home in 1860: Southern Division, Coosa, Alabama
Race: White
Gender: Male
Post Office: Wetumpka
Value of real estate: $2500, Pers. Estate: $3000
Household Members:
Name Age
Y D Harrington 42 B. Minister
Tiletha Harrington 42
Sophrona Harrington 19
Jas Harrington 18
Drury Harrington 16
Jeptha Harrington 14
Wm Harrington 12
Henry J Harrington 11
Matilda C Harrington 9
George Harrington 7
John Harrington 5
Emma Harrington 7/12
Monning Emfinger 65
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1860 United States Federal Census about Y D Harrington
Name: Y D Harrington
Age in 1860: 42
Birth Year: abt 1818
Birthplace: South Carolina
Home in 1860: Beat 3, Rusk, Texas
Gender: Male
Post Office: New Salem
Value of real estate: $1800 Pers. Estate: $5105
Household Members:
Name Age
W M Harrington 9
B N Harrington 2
Y D Harrington 42 M. D.
Mary R Harrington 31
H J Harrington 18
A E Harrington 16
H W Harrington 12