The name Kellen is a boy's name of German, Irish origin meaning "swamp; slender". Kellen is ranked #622 on our popularity charts and is often added to lists like Boy Baby Names Moving Up Fast and discussed in our forums with posts like "Heaven Hell or Purgatory- Boys".
From the experts:
Kellen is German in origin and Irish in spirit. Kellen has fallen a bit in popularity for boys since its peak in 2012, but it has possibilities for girls too. In fact, Kellen's similarity to such feminine names as Helen, Ellen, and Kelly makes it feel more unisex or even female, though Twilight actor Kellan Lutz has done much to popularize this name for boys.