There is a correct spelling of it...in Irish Gaelic it is Tir na nOg with a fada over the "i" and the "O" (I don't use fadas, as not all software can read them). Means Land of Youth.

The word "tir" in Irish means "land of" as in Tir Eoghain, County Tyrone.

Additionally, there are Tir Na mBan, Land of Women; Tir fo Thuinn, Land under the Wave; Tir na mBeo, Land of the Living, etc. All are found often in Irish myth, and are euphemisms for the Irish Otherworld.