They are called housemates.

I'm also from the US and I do hear people use the term housemate as well as the term roommate.

Hi Annette, “Roommates” is the most common term in American English, but unlike other answerers I don’t think “housemate” is unheard of. Maybe it’s just my generation or living with many students from around the world, though.

Americans do use "housemates". In college, a roommate is someone you actually share the room with, perhaps 1 to 3 other people in a dormitory room. If those people shared a house where everyone had their own room, they would use "housemates" to distinguish from the former situation. If there is any kind of confusion like that, people would use something other that "roommate", such as "someone who shares my apartment" etc. If no confusion were possible, people might revert to using "roommate" but "housemate" could also be used.

I’m a native from the USA. We never say housemates. We would use the term roommates no matter the dwelling but it implies that you are renting. You could use the term co-habitating if you are lovers renting a dwelling. Or you could say I co-own my house with a friend/lover if you are purchasing the home together.