If I'm reading the maps right that would be the SE corner of present day Route M (East Main St.) and South Water Street. The Hummel Property extended south to the creek. If you look at the satellite images it appears that the property as platted in 1930 appears to be intact and still farmed. You can just make out the railroad scar that transected the property Southeast to Northwest.

http://maps.google.com/maps?hl=en&source=hp&q=Truesdale+Missouri&um=1&ie=UTF-8&split=0&gl=us&ei=BJeiSrLRForQM4qRpN8P&sa=X&oi=geocode_result&ct=title&resnum=1

And yes I suspect the camp was named after Gen Merrill's wife. It was a good location from what I can tell.

John R.