From the Diary of Archibald Little Hager:
Hager Diary – February 5, 1866 – "One of the 2nd Missouri shot Joseph Pratte, Bernard Pratte’s son. Wound said to be fatal."
Hager Diary – February 8, 1866 – "Joseph Pratte died."

What military unit would have been in Perry County, Missouri in February 1866?

The 2nd Missouri State Militia had been mustered out in April 1865 and the 2nd Regiment Cavalry (Merrill Horse) was mustered out in September 1865 and the 2nd Infantry in 1864.
There are no editions of the Perryville Weekly Union available from July 1865 to August 1866.