After chatting with support, it looks like Retool (currently) hosts in Azure us-west-2 ( Washington).
Note: Couldn't find this information in docs or community so this may be duplicate information.
I just found out from support that the backup is in us-east-1 (N. Virginia).
Thank you so much for documenting this, @erichosick! Will sync with our docs team on making this even more visible.
We have a new doc on our hosting, architecture and configurations that should hopefully help answer this question for other users! It's also great that we have this post in case a user is looking for the specific hosting location.
the backup is in us-east-1 (N. Virginia).
Thank you again for your feedback here, @erichosick 
https://docs.retool.com/page/security#hosting-architecture-and-configurations