Garth opened with 4 wings, A-D, 25 years ago and holds long-term and indeterminate-sentenced prisoners. E wing opened in 1997 and houses a substance misuse therapeutic community and a drug recovery unit. In 2007 2 new wings, F and G, were opened and in March 2014 a 48-space personality disorder treatment unit (the Beacon unit) was opened, in conjunction with Merseycare NHS trust.
- A-D wings 133 each, wing B houses the Beacon Unit.
- E wing holds 118
- F-G hold 97 each