Per institution.
And there is a lot of consolidation.
So I would be careful.
It is really easy to be placing money into different banks, but essentially the same one.
A married couple each have 250k coverage for their personal accounts, and each have 250k for shared account(s), so they could in theory have 1M coverage at a single institution.
If you are married it is 500K, if you have a trust it is like 1.25M. 250K for each beneficiary up to 5 (or something like that).