George W. Uselton/Usselton, served with Company B, 3rd Tennessee Volunteer Infantry, in the War with Mexico (1846-48).
The Third Tennessee Volunteers was commanded by Colonel Benjamin F. Cheatham (later a Confederate general) was organized in late 1847, and disbanded in July, 1848.
A family history from 1981 suggests a George Uselton went to Illinois during the 1860s, and in some manner supported the Union cause.
A John W. Uselton (d. 1933) served in Company C, 31st Illinois Volunteers during the 1860s. Buried in Gallatin County, Illinois.
In the 1880s George W. Usselton associated with other United States Veterans in reuniion at Gallatin County, Illinois, but as a veteran of the Mexican War...
From 1887, in Illinois, George Usselton received a pension for his Mexican War service. US Mexican War Pension filing number 6,572, Certificate number 12,128, and there is a Widow's Pension application number 162033, and certificate number 12,788.
US Veterans Pensions were not provided to anyone who in any manner, "voluntarily engaged in or aided or abetted the late rebellion against the United States" of the 1860s.
Interestingly, there are other pension application files relative to veteran application no. 6572, for a George Uselton of Tennessee, which suggests service under an alias of "Brown" under an officer named Newman in a Tennessee cavalry unit in the War with Mexico as well.
Perhaps reference to Col. Jonas Thomas' Regiment of Tennessee Mounted Volunteers (aka 1st Tennessee Mounted Infantry), whose Company D was commanded by Capt. L.D. Newman. The Regiment serving from June, 1846 to May, 1847 (mustered out at New Orleans). There was a Pvt. "Joseph Brown" in that company.
The Federal Pension application records noted above (which would be at the National Archives) should have lots of information about George Uselton.