The police recorded 86.0 crimes per 1,000 people a year in Ystrad Mynach from September 2023 to August 2026, 13% higher than the typical town's 76.2. The most common was violence and sexual offences, at 42.4. In the 12 months to August 2026 it was 91.3, up from 85.3 in the 12 months to August 2024.