The place where your ancestors lived in 1911 was Glackaundarragh. That’s a townland. A townland is an Irish administrative district. And there frequently isn’t a town in a townland. It’s often just agricultural land. It is in the civil parish of Inishmagrath.
You can see where it is by using the maps on the Griffiths Valuation site:
It’s on the Sligo & Leitrim border a few miles west of Lough Allen, near Corry Mountain. You may need to ask locally to find it. You probably won't find it on the average satnav.
In 1857 there were 6 different Leyden farms in the townland (out of a total of 26 properties). Which of those is the one that your ancestors lived in in 1911, I couldn’t say but you could find out by looking at the Valuation Revision records in the Valuation Office in Dublin. (They are not on-line yet). They used the same plot numbers as Griffiths so it should be relatively straightforward working through the records to see which is which. The Griffiths contemporary maps delineate each property and so you can use that to locate them today. A little patience is required to get the hang of it.
In 1911 there were 27 houses in the townland. 8 of them were occupied by Leydon/Leyden households. That may take a bit of sorting out! Total population of the townland then was 142.