Federal elections in the United States are run by states and, in practice, by counties. That decentralization is the reason voting procedures differ so much across short distances.
Administration sits below the federal level
Federal law sets certain floors and protections, but the mechanics of registration, ballot design, polling places and counting are determined by state law and executed locally.
County or municipal election officials handle voter rolls, staffing and equipment. Two counties in the same state can differ in wait times, early voting sites and ballot layout.
This structure predates modern national campaigns and is why there is no single national procedure a voter can learn once.
Registration rules create the first differences
States differ on registration deadlines, on whether registration happens automatically through motor vehicle agencies, and on whether same-day registration is available at the polls.
List maintenance rules also vary. Registrations can be marked inactive or removed after periods of non-voting or returned mail, under procedures set by each state.
The practical consequence is that a voter who has moved, married or changed name should verify their registration rather than assume it carried over.
Identification requirements are not uniform
Some states require photo identification, others accept a broader set of documents, and others rely on signature matching against the registration record.
Where identification is required, states generally provide alternatives such as provisional ballots that are counted once identity is confirmed within a set period.
Provisional procedures differ in how long a voter has to cure the ballot and what documentation is accepted, which affects how many are ultimately counted.
Mail and early voting operate on separate rules
Availability ranges from no-excuse mail voting to systems requiring a stated reason. Some states mail ballots to all registered voters automatically.
Deadlines differ on whether a ballot must be received by election day or only postmarked by it, which changes how early a voter must mail it.
Signature verification and cure processes vary as well, and ballots are sometimes rejected for procedural reasons unrelated to eligibility.
Where to confirm current rules
Because rules are amended frequently and litigated between elections, information from a previous cycle is unreliable even within the same state.
State secretaries of state and county election offices publish current requirements, deadlines and polling locations, and are the authoritative source.
Nonpartisan voter assistance organizations also maintain state-by-state summaries, which are useful for orientation before checking the official source.