Which classification system is used by most police departments in the U.S. for fingerprints?

The Henry's classification plan is widely recognized as the foundational system used for organizing fingerprints in many police departments across the U.S. This method categorizes fingerprints based on specific patterns present in the ridges, which are grouped by the presence of whorls and loops.

Developed in the early 20th century, Henry's system allows for systematic filing and retrieval of fingerprint records. It assigns numerical values to the patterns found in an individual's fingerprints, enabling law enforcement to efficiently compare a suspect's fingerprints against those in their database.

While the FBI classification system is an adaptation of the Henry system for federal use and AFIS (Automated Fingerprint Identification System) represents modern technological advancements in managing and analyzing fingerprints, it's the original Henry's classification plan that remains the fundamental technique utilized by many local and state police departments to classify and organize fingerprints for comparison and identification purposes. The whorl and loop system describes types of fingerprint patterns rather than a classification system itself, making it less comprehensive for the context of this question.