I was only able to find Herman Jr. in the military.

1860 United States Federal Census about Herman Gellert
Name: Herman Gellert
Age in 1860: 12
Birth Year: abt 1848
Birthplace: Missouri
Home in 1860: Boeuf, Franklin, Missouri
Gender: Male
Post Office: Campbellton
Value of real estate: View Image
Household Members:
Name Age
Godfred Gellert 57
Margaret Gellert 34
John F Gellert 14
Herman Gellert 12
Elizabeth Gellert 11
Mary Gellert 9
Caroline Gellert 7
Edward Gellert 1
Louis Koester 22
Frank Meka 20
Henry Hagerman 23
Fred Lewroster 25
John Exline 28

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1900 United States Federal Census about Herman Gehlert
Name: Herman Gehlert Farmer
Age: 73
Birth Date: Mar 1827
Birthplace: Germany
Home in 1900: Union, Franklin, Missouri
Race: White
Gender: Male
Relation to Head of House: Father
Marital Status: Widowed
Father's Birthplace: Germany
Mother's Birthplace: Germany
Occupation: View on Image
Neighbors: View others on page
Household Members:
Name Age
Fritz Gehlert 32
Anna Gehlert 26
Elenore Gehlert 2
Herman Gehlert 73

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Herman C. Gehlert, Private, Company D, 47th Regiment Missouri Infantry, enlisted August 27, 1864 at Pilot Knob for 6 months, left sick in hospital at Nashville, Tenn. being admitted December 24, 1864, returned to duty February 1, 1865, mustered out at Benton Barracks, Mo., March 30, 1865, description: grey eyes, brown hair, light complexion, 5' 8", 17 year old Farmer, born in Franklin, Mo.

M405: Compiled Service Records of Volunteer Union Soldiers Who Served in Organizations From the State of Missouri.

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Forty-seventh Infantry
MISSOURI
(6 MONTHS)

Forty-seventh Infantry. -- Cols., Thomas C. Fletcher, Amos W.
Maupin, Lieut.- Cols., Amos W. Maupin, John W. Fletcher, Maj.,
John W. Emerson.

In Aug., 1864, Gen. Rosecrans authorized Col. Fletcher to
organize a regiment in southeast Missouri, for service in that
part of the state. Through the efforts of Fletcher and his
assistants more men were recruited than was necessary for the
completion of the 47th, and the surplus was turned over to the
50th Mo. infantry. The regiment was mustered in for six
months, and until Dec. 12 was on duty in the state.

It was then ordered to Nashville, Tenn., where it arrived
three days after the Confederates under Gen. Hood had been so
ingloriously defeated. It remained on duty at Columbia,
Spring Hill and Pulaski, Tenn., until the latter part of
March, 1865, when it was ordered to St. Louis, where it was
mustered out on the 29th and 30th of that month.

During its service in Tennessee it was under command of Col.
Maupin, Fletcher having been elected governor of the state in
the fall of 1864.

Source: The Union Army, vol. 4, p. 271