Barbara

George W. Heifner was the son of Bartholemew and Polly Heifner both from Kentucky. 1850 Census has them in Randolph County Missouri Dwelling 531.

In the household:
Bartholemew 42 KY
Polly 42 Ky
John 21 Indiana
Jacob 16 MO
Thomas 13 MO
Emily 10 MO
Eliza 9 MO
Margaret 7 MO
George W. 2 MO

Thomas Heifner served 3rd Missouri Battery Light Artillary CSA enrolling in Randolph County in 1862. This was also know as Lowe's Missouri Battery.

Randolph County as you may know is next door to Howard County home of the Cooley family.

The George W Heifner in the MO SOS files that served the Union in the 16th MO Vol. Cav. and the 73rd EMM was enrolled in Lebanon in Laclede County MO. I do not think that he is the same George W. Heifner of your family line. he has a brother Silas who also served in the 73rd EMM and Silas was from Dallas County MO, adjacent to Laclede County.

The 1860 Census has the family remaining in Chariton Township, Randolph County, MO Dwelling 101

B. Hefner 52 KY
Minerva 42 VA
Margarett 16 MO
George W 13 MO
Ann G 11 MO
Mary 7 MO
Martha 5 MO
Lewellen 3 MO
Elizabeth 2 MO

Given ages I suspect Minerva was a second wife and some of the younger children may have been hers from a prior marriage.

1880 Census has George W Heifner with wife Sarah E living in Chariton Township Randolph County MO dwelling 129.

Given the known birth dates of Sarah Cooley and Geeorge W Heifner I sincerely doubt that either were ever actually enlisted in a military unit during the civil war.

Hope this helps.

John R.