Ask “how long does an ALPR read stick around” and the honest answer is: it depends entirely on where the camera is and who runs it. There’s no single national retention rule. What exists instead is a wide range set by a mix of vendor defaults, state law, and individual department policy — and the range spans from minutes to indefinitely.
Why retention length matters
A single plate read isn’t very revealing on its own. The privacy risk grows with how long reads are kept and how many of them accumulate. A database holding 30 days of reads can only reconstruct a month of someone’s movements. A database holding years of reads can reconstruct patterns of life — where someone works, worships, seeks medical care, or spends nights — which is exactly the kind of aggregation concern researchers and courts have focused on. For more on the legal side of that argument, see Your rights when it comes to license plate tracking.
The shortest end: minutes
New Hampshire sits at the extreme short end. Under state law, ALPR data must be purged within three minutes unless it matches a hot list — one of the strictest retention limits in the country, and a useful illustration that short retention windows are technically and operationally workable, not just theoretical.
The vendor default: 30 days
Flock Safety, the largest single ALPR vendor in the US, publishes a default retention policy of 30 days on a rolling basis, enforced through an automated cloud lifecycle policy, unless a customer agency configures something different under its own state law or contract terms. Thirty days has become something like an industry-common default across several vendors, though it is a default that customers can and do adjust — both up and down — depending on state law and local policy. See How Flock Safety’s camera network works for more on how that default is enforced.
State-mandated windows
Where states have passed ALPR-specific statutes, retention limits are one of the most common things they regulate. A few examples we could confirm:
- Maine: 21-day retention limit under 29-A M.R.S. § 2117-A.
- Virginia: system data purged after 21 days; audit-related records may be kept up to 2 years.
- Illinois: general data archived after 90 days, extendable up to 5 years if tied to an active investigation.
- Arkansas (2025 law): non-governmental ALPR data must be deleted within 60 days; state agencies and parking enforcement may retain data up to 150 days.
See our full state-by-state legal overview for more states and the limits of what we could verify — most states don’t have a statutory retention limit at all, which means retention is set entirely by department policy and can vary block to block.
The long end: indefinite
Before state laws started catching up, the ACLU’s 2013 nationwide survey — built from roughly 600 public records requests across 38 states — found that many departments were storing data on innocent people for years, or with no expiration date set at all, regardless of whether any read was ever tied to a crime. Where no statute or vendor policy sets a hard limit, “how long is data kept” often reduces to “as long as storage costs allow” — which, given falling cloud storage prices, keeps trending longer rather than shorter.
What determines retention in practice
For any given camera, retention length is usually the product of three separate decisions, each made by a different party:
- The vendor’s default setting — what the platform ships with out of the box.
- State law, if the state has passed an ALPR statute (most haven’t — see the state overview).
- The individual agency’s own policy, which can extend or shorten the vendor default within whatever the state allows.
That layering is why two departments running the exact same camera hardware, in neighboring counties, can have completely different retention windows.
How to find out what your local department does
Retention policy is typically a public record, even where the underlying plate data isn’t. A public records request to your local police department or sheriff’s office asking for their “ALPR use and retention policy” is usually enough to get a direct answer, and it’s a more reliable source than assuming a vendor’s marketing default applies. For more on the practical options available to residents, see Can you opt out of license plate reader surveillance?, and browse the camera map to see documented cameras near you.