The four were arrested on Friday last week after a 32-year-old Scarborough woman was stopped and searched in the street in Eastfield and arrested on suspicion of supplying class A drugs.
A search was then carried out at a property in Eastfield and another three people were arrested on suspicion of supplying class A drugs.
They include a 38-year-old woman from Scarborough, a 26-year-old man from Liverpool and a 39-year-old man from Manchester. The two men have been released on bail while the investigation continues. The two women have been released while under investigation.
This latest activity follows the arrests of 15 people across the county since the beginning of October as part of a crack-down on county lines.
North Yorkshire Police said: "County lines is the name given to a type of organised crime in which drug dealers from urban areas such as Manchester, Liverpool and West Yorkshire, exploit children and vulnerable people and force them to travel to smaller towns such as Scarborough, York and Harrogate to sell drugs. Often using violence and intimidation. It takes its name from the phone lines used to communicate between towns and advertise drugs for sale.
The dealers at the centre of county lines also use violence and threats to take over the homes of vulnerable people, often drug users themselves, or people with mental or physical disabilities, to store and sell drugs in a tactic known as “cuckooing”."