Now this is probably not your Uncle Joshua Ferguson as you say he was in Arkansas after the war,but I did note this fellow in the Worden Cemetery north of McKinney.
Joshua Ferguson 1841-1864
Also a Johsua Ferguson married a Synthia B.Kelley Sept.19,1860 in Collin Co.
And also obviously your Fergusons left Collin County either during or after the war as they are not on the 1867 County Tax or Voter Registration List.
MWT