Yes, 'The Watcher' series is based on a true story. It was inspired by the real - life case of a family in Westfield, New Jersey, who received creepy and threatening letters from someone calling themselves 'The Watcher' after they bought a house.
The Watcher series is purely fictional. It's crafted by the imagination of the writers and not drawn from actual happenings. The storylines and characters are made up for entertainment purposes.