Unlike Europe, where ownership in closely held businesses must be disclosed in some record kept with a notary as a "public" record, the U.S. norm is that ownership is only maintained in the internal records of the company or by certificated (usually negotiable) shares. The company needs to know who the owners of record are for lots of practical purposes like knowing where to send dividend checks and notices of owner meetings, and tax compliance. But the public doesn't in most cases.
C corporations are more private, because if you don't pay dividends, you don't need to know who the members are for many tax purposes, whereas the IRS has to be told every year who the owners of passthrough taxed entities are.
Most states require at least a registered agent but many states allow a registered agent to be an entity (something that some states require a license for and others do not) and some allow a company's principal office to be its registered office with it serving as registered agent for itself. Those states usually allow for service of process by mail in those cases. If determining ownership was necessary, the entity could be served with process by whatever means are authorized by state law with a subpoena.
Some states require that at least one manager or officer or director name be disclosed publicly, but there is probably a 50-50 split on that. Many do not.
It looks like in PA you must disclose the organizers of an LLC (who don't have to have any ongoing role in the entity - for example, it could be a lawyer who drew up the paperwork), and a registered agent (which may be an entity), but not owners, managers or officers.
There is international pressure for the U.S. to pass a law or enter into a treaty requiring ownership disclosure, in order to discourage illicit use of these entities, but it doesn't seem to be going anywhere.