There are approximately 150 different board designs in Monopoly Go currently. However as the game evolves we would expect that number to increase.
Although there are 150 boards, you may not get to see them all because all players are put into different board groups which have anywhere from 100 to 150 different boards in them. This is to allow things such as localization of boards around the world.
You also may not get the same level names as other players. While the cost of each level is more or less the same no matter which group you are in, the level designs and the order you get the boards in can be different especially after you get past the first hundred boards.
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