We finally learned on another visit to Ireland that the "Mountain Hill" is in Cormoy townland in Aghabog parish. It has 196 acres and is in Clones Poor Law Union (Civil District), Dartree barony. As you drive on the R189 northeast out of Newbliss, turn left onto L6150; driving up the hill on L6150, Cormoy is the farmland and hillside to the right.
William Johnston (whose wife was Eliza Jane Calvin) held lots # 9 & 10 in Cormoy at the time of Griffith's Valuation. This was just over 20 acres with house, offices and land. The landlord for most of Cormoy, including the Johnston farm, was Lord Rossmore.
Wm. & Eliza Jane's daughter Eliza Jane Johnston married George Freeland in 1869 -- son of neighboring farmer John Frieland (Freeland) who held lot #10 at the northern point of Cormoy in Griffith's Valuation. The Freeland farm was 18+ acres with house, offices and land.
Another daughter married a neighbor: Maria Johnston married the widowed Thomas Graham in 1874, son of Griffith's landholder James Graham of Cormoy. James Graham held over 30 acres with house, offices and land.
William & Eliza Jane's daughter Anne Johnston married Ebenezer "Eben" Wilkin in 1857, and moved to Ematris parish where they lived the remainder of their lives.
Other children of Wm. Johnston and Eliza Jane Calvin include Joseph Johnston, born 1845, and John Johnston, born 1855, both baptised at Newbliss Church of Ireland. I haven't yet discovered if these sons lived to adulthood, married and had children.
I'm always glad to share research notes so that we can help each other fill in the blanks on our family trees.