Conas atá sibh go léir?
I'm of the surname O'Loideáin and guess where I'm from? County Sligo Ireland.
The anglicised forms of the name vary and include Leyden, Leydon and Lydon, probably Layden and others too.
Leyden and Leydon are concentrated mainly in Sligo though also in Mayo
There are many with this name in Sligo that I know of, unrelated to myself
Lydon is mostly concentrated in Galway and Claire
That these names are all concentrated on the western coast of Ireland and all share the same gaelic root suggests that it is an Irish gaelic name in origin
Many gaelic names are derived from colours and Liath means grey
The name Liath comes from the Irish mythology of Fionn Mac Cumhail
There is also the Irish legend of LIADAN the poet
"I am Liadan
Who loved Kurithir,
It is true as they say.
"The music of the forest
Would sing to me when with Kurithir,
Together with the voice of the purple sea."
I have heard of the possible connection with a town in Holland called Leiden, but this seems unlikely given the geographical isolation of the name
Hope this helps