Forces across England and Wales have amassed data about people who dial 999 or non-emergency numbers to report their concerns or pass on information.
West Midlands Police, the second largest force, holds 1.1 million records of people who have reported offences over the past 12 years.
Others, including Lancashire, Cleveland, Avon and Somerset, Gloucestershire, West Mercia and North Wales, hold more than 150,000 each.
Senior officers admitted the information could be used against people as part of any future police investigation.
They insisted gathering the data was necessary to fight crime, protect the vulnerable and ensure concerns were dealt with properly.
But critics said the vast databases were further evidence of a creeping database state in which information on the innocent was held alongside criminals and suspects.
Evidence of the police databases was collected in a series of requests by the Press Association under the Freedom of Information Act.
A total of 13 forces responded with details revealing how they held between 10,091 records (Lincolnshire) and 1,147,413 (West Midlands).
Those with the biggest databases were Lancashire (around 600,000), North Wales (302,754), Cleveland (172,369) and Avon and Somerset (162,968).
The majority of forces said it was not possible to collect the information because the scale of the task was too big.
Hertfordshire said it held 1.6 million records of all kinds generated since 1989 while Sussex said it held 5.6 million records gathered over seven years.
These records included details of millions of victims of crime as well as suspects and offenders.
Forces said personal information was spread across up to 22 databases and warned details of the same person could be recorded several times.
They said staff and officers were following guidance published by the National Policing Improvement Agency (NPIA).
In some cases, police staff not only record names, addresses and contact details, but ask about the callers' date of birth and ethnicity.
Gus Hosein, of Privacy International, said: "There's a point where the police stop seeing members of the public as the people to be protected and rather see them all as potential criminals."