The police recorded 38.7 crimes per 1,000 people a year in Harleston from September 2023 to August 2026, 49% lower than the typical town's 76.2. The most common was violence and sexual offences, at 23.0. In the 12 months to August 2026 it was 43.3, up from 37.7 in the 12 months to August 2024.