Hi Jerzy
A quick reply. When I was a child, land north of the river Forth from our farm on the Stirlingshire and therefore south side, was regarded as Perthshire. Thornhill is in Stirling Council's administrative area but I'm almost sure you'll find it under Perthshire 100 years ago.
I also found a document by searching Macorriston farm. It described an axe head in the collection of Smith art gallery and Museum in Stirling, found by George Paterson of Macorriston Farm in 1902.
Good luck
Mary