The film is set around Caledonian Road in London where notorious drug teenage dealer Henry Hicks was active, until he was knocked of his scooter while running away from the police.
County Lines is a British term denoting taking drugs or cash across town, City or County boundaries into another area, typically using vulnerable people and children as the mules - making it harder for drug enforcement agencies to track back up the supply chain to leaders. It may also make enforcement more difficult as not all authorities have jurisdiction everywhere. County Lines is also known as Going Country / OT / Going Cunch.
Writer/Director Henry Blake drew on his experiences as a youth worker for 11 years, thus the true story the film is based on is more an amalgamation of different people and events rather than a specific one.