I actually don't know the answer to this, other than to say that I've noticed people in their reviews bitching when something isn't made in the USA. Whether that's because of an actual lack of quality, or just unmet expectations, I'm not sure.
I'd like to buy a few of their jackets, but the fit is just huge on the ones I've tried on. So the only clothing I have from them is the Levis x filson trucker jacket and 505 tin cloth pants.
Thanks. Just found out they discontinued the tin cloth lined shirt a few days after I purchased mine.