In 1908, Grahame retired from his position as secretary of the Bank of England. He moved back to Berkshire, where he had lived as a child, and spent his time by the River Thames doing much as the animal characters in his book do -- as the book says, "simply messing about in boats '' -- and expanding the bedtime stories he had earlier told his son Alastair into a manuscript for the book.
what river is in wind in the willows
River Thames