The Poldark novels are fiction. They do draw on historical events and settings to some extent. For example, the mining industry in Cornwall during that era was real, and the social and economic conditions were based on historical facts. But when it comes to the individual dramas of the Poldark family, the romances, the feuds, and the adventures, these are fictional elements. The novels blend historical context with fictional storytelling to create an engaging and fictional world.
The Poldark novels are fiction. They are set in Cornwall during the late 18th and early 19th centuries, which gives them a historical backdrop. However, the main plotlines, the relationships between the characters like Ross Poldark and Demelza, are fictional constructs. The author, Winston Graham, used his knowledge of the time period to create a vivid fictional world that has elements of the real Cornwall at that time, but overall it is a work of fiction.