Surname 
After many years JW has finaly given Faith a last name and - it is the Irish name of Lehane.
It’s a variant of the name: Lyons
Other variants are: O’Lyne, Lane
Counties in which this surname is most commonly found: County Mayo
[ taken from: IrishGen.com ]
I may be wrong, but I believe it’s after Dennis Lehane - the author who wrote the rather brilliant ‘Mystic River’ (the novel is set in South Boston and is now an awesome movie that was filmed in and around Boston).
To be blatantly honest, while the name is growing on me, I find the choice a lazy one. It’s as though Joss said “I think I’ll name her after a writer - let’s see if there are any from South Boston. Oh! There is! - his name is Lehane so that’s what I’ll call Faith”.
There’s no irony, no sense of the name being from the Buffyverse - there’s nothing ‘Faithy’ about it at all - which I find an honest disappointment and letdown - (something Whedon is doing to me quite often lately if truth be told).
For the years that Faith graced our screens, she was bereft of a surname. While some found it annoying, there was a reason. Basically, it was so you felt more for the character of Faith if she was totally isolated from everyone. Depriving her of a last name meant she really has no connections to anyone at all. She hadn’t (and still hasn’t as far as I know) any family to fall back on. Also, it made Faith ‘adoptable’ to us - the viewers and fans. Any one of us could take her in and care for her (and many of us wanted to).
Now, however, she’s Faith Lehane of South Boston.
At least she’s Irish ;)
More information on Lehane: In 1890 Lyons was the 80th most numerous surname with approximately 9, 400 bearers. There was a sept of the Lyons in the barony of Kilconnell in Galway. Another sept was located near Kill in Kildare. A third branch called O Liathain was anglicised as Lyons in Cork. O Liathain means ‘descendant of Liathan’ which is a diminutive of Liath meaning ‘grey’. The surname Lyons may also be derived from the Norman surname ‘de Lyons’ which possibly originated from Lyons-de-Foret the place-name in France.