Yes, you can have four of a kind in Mahjong Island. Four identical tiles make a Quad (called a kong in traditional mahjong). It counts when the hand you are building on the Island Card asks for one.
When does a Quad count?
The Island Card is Mahjong Island's own card of hands. Each hand is written as groups of identical tiles, like a Pair (2), a Set (3), or a Quad (4). You win by completing 14 tiles that match one line on the card.
To see how the hands are written, read how the Island Card works.
Can a Joker fill a Quad?
Yes. A Joker can stand in for a tile in a Quad. Jokers can fill a Set, Quad, Quint, or Sextet. They can never fill a Single or a Pair.
Learn more in the guide to Mahjong Island Jokers and Bonus Hands.
Can you take a discard to make a Quad?
Yes, if a hand on the card still allows it. When another player discards, you may take that tile (Take Tile) to make an Open Group of 3 to 6 identical tiles. That Quad then goes face up as an Open Group.