Adafruit does their own assembly (pick and place / reflow) but not sure what PCB providers they have. There are US based PCB fabs.
Cyber City Circuits does small scale assembly in the US and seem like a cool company (ran into them from the Datasheet Digest podcast they put out). But yeah obviously they aren’t going to be able to match a $35 PCBA JLCPCB prototyping order.
I can tell you from first hand day job experience:
Electronic manufacturing in the US definitely exists. It also is low quality and 5x to 10x the cost of China.
An assembled board that costed us $825/unit in the US (and frequently had errors) costs $130/unit from China and they nailed it every time (probably because they machine QC rather than human QC). It's really not even close. Same goes for machined parts - drastically cheaper and higher quality from China.
Cyber City Circuits does small scale assembly in the US and seem like a cool company (ran into them from the Datasheet Digest podcast they put out). But yeah obviously they aren’t going to be able to match a $35 PCBA JLCPCB prototyping order.
https://cybercitycircuits.com/