Aye, as they say, farm-able tiles are decently common. Though, less common than tiles that allow you to build houses/factories. Farms can be difficult to maintain, and you're usually not going to have lots of them up at once. Even so, it's not very hard to get a few going and stockpile tons of food.
Though, the actual "farmland" tile IS rare. You wont see those very much. They do produce the most food per turn though. (also, try entering them when you do find them.... there's perk tokens inside!)
The best thing you can do though when learning the game is that every time you encounter any type of tile you havent seen before, go over to it and bring up the menu, as it'll tell you exactly what it does, and exactly what you can build on it. Since there's a HUGE number of different tiles, doing this is really important.