Every county in the United States collects some form of data on registered voters. Most states then aggregate the data from each of their respective counties. Voter data typically includes a voter's name, address, and the history of which statewide and national elections the voter participated in. Some counties also include phone numbers, email addresses, political party preference, municipal vote history, and other demographic information.
The exception is North Dakota. It is the only U.S. state that does not require voter registration. Instead, North Dakota collects a list of voters who cast a ballot in a particular election.