I am most familiar with California's rolls since I have been investigating them for years, but every other state has similar contents. In addition to the names and addresses of people qualified to vote, most rolls also contain birth dates, mailing addresses, voting history, party preference, date of registration, birth state or country, and even phone numbers and email addresses if available.
If that weren't enough, this information is maintained in the rolls not only for active voters who can vote, but also for "cancelled" voters who have moved away, who have died, who haven't voted for many years, people who became ineligible by committing a major felony, ones who have been declared incompetent, and ones who requested removal. Registrations that are cancelled are not to receive election mailings, and votes are not to be counted for them.
There is another category of registration in the rolls for "inactive" voters. These are registrations that can still vote, but will not receive election mailings, including mailed ballots. Yet a fourth category is that of "provisional". These are typically registrations that for some reason are incomplete, such as missing a signature sample, or are a preregistration for someone not yet old enough to vote.
Once entered in the rolls, it is almost impossible to remove a registration It is, however, very easy to convert one to another as the change of a single letter in the database is sufficient. A change from "C" to "A" can make a cancelled registration an active one whose vote will be counted. This creates lots of opportunities for both honest errors and dishonest manipulations.
While local county officials are charged with maintaining their voter rolls, the reality is that they have little or no control over the contents. In California, as in most states, there is a master voter roll database. In order to handle such things as DMV registrations, moves between counties, and other changes, the state maintains master rolls. Updated copies are periodically returned to the county.