The traditional home place of the Ryan Clan is Owney & Owneybeg in Counties Tipperary and Limerick and Idrone in Carlow.
This map below helps show where these are in Ireland.
This great website below shows the distribution of the surname Ryan across Ireland in the 1901 and 1911 censuses. You can see that it has spread from these traditional areas and is now the number one surname by number in Tipperary and Limerick.
There are of course Ryans from all across the country and other prominent places include Roscommon (O’Mulrennan), Galway / Mayo (O’Ruadhains / Ruans) and Galway (MacRyan) from where those bearing the name originate.