There are many types of yetis. The most common originate from the Himalayan Mountains. In Monster's Inc., the Abominable Snowman appears. He is the most famous of their kind.
The Yetis' cousins, Bigfoot, originates in the Pacific Northwest. Bigfoot is incredibly shy and doesn't like being photographed.
Yetis have recently moved from the Himalayan Mountains to Ohio to be closer to their emo relatives (Bigfoot). How did they get there without being spotted? In their UFOs, obviously!