Ken, the 1884 map shows the location East of Ft Cobb in a horseshoe bend of the River or close to it.

The 1982 map shows the horseshoe bend in the small community of Washita.

The community or Wichita Village is located on the 1884 map near the same area of Sterling Ok., on the 1984 map. Too far South of Anadarko or the Washita River.

I will personally say from your identifiers, that the Wichita Agency is located in between the towns of Ft Cobb and Anadarko at the PSO town of Washita on the Washita River. The County road is called the Indian Road which is North of Freedom School running East and West. I used the Indian Road transporting prisoners from Ft Cobb to Anadarko, it was closer than taking #9 hwy from Ft Cobb State Park. there is a County road leading to Washita from Hwy #9 not more that 5 miles max.

http://www.lib.utexas.edu/maps/historical/ok_indian_territory_1884.jpg

http://www.okladot.state.ok.us/hqdiv/p-r-div/maps/state-maps/pdfs/1982.pdf