The B Reactor of the facility produced the plutonium used for Trinity and Fat Man, and then for many more thousand bombs during the Cold War. More precisely, this was done at
Located in Washington, in a dry place the middle of the mountainous areas of the Western United States, where basically no one lives. The Columbia river is however nearby, that river is quite large, and provided the water needed by their activities, notably for cooling the nuclear reactors. It is worth it having look on Google Maps to get a feel for the region.
Unlike many other such laboratories, this one did not become a United States Department of Energy national laboratories. It was likely just too polluted.
Bibliography:
Aerial image of the Hanford site in 1960
. Source. 
This was one of the two American plutonium production sites, together with the Hanford site. www.youtube.com/watch?v=qwKhz7BPBLY mentions it produced about 1/3 of the total American plutonium.
www.reuters.com/article/world/americas-nuclear-headache-old-plutonium-with-nowhere-to-go-idUSKBN1HR1JT/ claims that as of 2018 it stored the majority of the plutonium stockpile of the country.