Based on talking with family back in Utah and from reading reports from around the US, I don't think people in the US are wearing masks to the same extent as Japan.

I would guess, 99.9...% of the people here wear masks anytime they will be in close proximity to others (work, stores, restaurants, schools, trains, walking down the street, etc). In fact, there are those who even wear masks in the outdoors. I went fishing a couple of weeks ago, and it seemed that a large % of those there were wearing masks.

I don’t know if the masks really do slow the spread, but there seems to be a strong correlation that they do.