I’m using Chrome. USA isn’t in the drop-down menu of Places when I am in Identify mode.
The state of Oregon is also missing. If USA and OR are missing, I’m guessing others are as well.
I just had a similar problem with the state of Ohio.
Texas is missing as a Place in Identify, too. Though I suppose it’s possible that it has finally seceded from the USA…
I can confirm the issue for the states. I can still get the United States in Identify, and it does work. It is my default, but I can also get to it after switching to another location.
I was able to get the state of Ohio when I finally gave in and typed “Ohio, USA” but it wouldn’t pull it up before that.
We’re taking a look.
Same issue(s) here. Two temporary workarounds: (1) Type, for example “Ohio, US” and it’ll pull up the state (like @m_whitson mentioned); or (2) You can enter the location ID directly into your query, like this https://www.inaturalist.org/observations/identify?place_id=31.
Last night, right before the planned downtime, I was in Identify mode ID’ing Texas plants. Right after the planned downtime I tried to do some more, but Texas was missing from the menu of places. I decided Texas temporarily missing was surely a feature, not a bug, and went to bed. 
Anyway, perhaps related to something done during the downtime?
Some places were not indexed with a search rank when we came back online. We’re reindexing them now. US and US states are looking pretty good, other places will be improved throughout the day. Sorry about this!