I know that in certain countries like Japan or South Korea: it’s normal to leave the front door unlocked since the probaility of someone breaking in is low since their crime rate isn’t high. I knew a friend of mine who resides in Korea where they even left the car unlocked with the keys inside, can you do either of those things in America?
Like others have said, it depends on where you are in the US. I live in a suburban area and we always lock our doors, whereas my cousins live in a rural region of the state and rarely lock their doors.
It’s up to you, but I’d always err on the side of caution and lock the door.