New Haven is a city in Franklin County, Missouri, United States. The population was 2,414 as of the 2020 census. New Haven is within th…New Haven is a city in Franklin County, Missouri, United States. The population was 2,414 as of the 2020 census. New Haven is within the Hermann AVA. New Haven was originally called Miller's Landing, and under the latter name was platted in 1855. A post office called New Haven has been in operation since 1858.