You’ve already worked it out but for anyone interested, it’s an old Gaeilge name likely coming from the Garilge word for church, Cill (meaning hard k) and the diminutive suffix - ín, so it means ‘lil church’
According to le Google, it's pronounced 'kil-ee-an', so a 'hard c'. I've always said 'sill-ee-an', but I also have never heard it said aloud so --shrug--
I big phat linguistics and etymology nerd, so i love looking that stuff up. It's Irish so yeah, hard 'K' sound.
Get lost down the rabbithole of etymonline. I just wish there were more resources for languages that aren't daughter-languages of P.I.E. But the answer to that honestly is to just learn a language like Finnish and read the sources for Proto-Uralic. Sigh, so much to learn!!