Three people have been arrested in police raids linked to drugs and mobile phones seized at HMP Garth in Leyland.
Lancashire Police worked with Greater Manchester Police and Cumbria Police to search five homes at around 6am on Tuesday.
Search warrants were executed at four addresses in Manchester and one in Cumbria.
Around £5,000 in cash and three vehicles were seized.
A 41-year-old man, a 54-year-old man, and a 24-year-old woman, all from Manchester, were arrested on suspicion of conspiracy to supply Class B drugs and taking prohibited articles into a prison.
All remain in police custody where they are being questioned by detectives.
The arrests come after police seized drugs and mobile phones at HMP Garth in September last year.
Det Sgt Nick Hills, from Chorley CID, said: “We are committed to tackling the supply and use of drugs across Lancashire and further afield.
“We work closely with colleagues from other forces as well as the prison service to combat drug supply and to take action against anyone we suspect to be involved with them.
“I would urge anyone who has any information about drugs to tell us so that we can continue to take action.”
Information about drugs can be reported to the police on 101 or to Crimestoppers anonymously on 0800 555 111.