NHTSA estimates that approximately 96 percent of model year 2013 passenger cars and light-duty vehicles were already equipped with EDR capability. The significance of this measure is in the specifics of what data it requires such devices to collect and its guidelines for how the data should be accessed. - Black Box 101: Understanding Event Data Recorders

Event Data Recorder - Supported Vehicle List

I will debate part of what the previous poster said, in that EDRs are technically optional, as there doesn't seem to be any US law that requires them.

But automakers benefit from the data they provide, so I'd expect just about every new car contains one.

We know for a fact Tesla, for example, uses Video Event Data Recorders, and they have near total access to any footage recorded by the vehicle at any time. That's one big reason I'd never buy one.