Readlyn is a city in Bremer County, Iowa, United States. The population was 845 at the time of the 2020 census. It is part of the Waterloo–Cedar Falls Metropolitan Statistical Area. The city is known for its culture surrounding the "Grump", a title of honor and area folklore character inspired by a real resident of Readlyn in the early 20th century. A post office opened in Readlyn in 1904.