Many public libraries host letterboxes (often letterbooks) on an official or quasi-official basis. Some even create special programs for children using letterboxes to encourage reading and deductive reasoning skills.
- Oneida (NY) Public Library
- Harrison (OH) Library
- Kimball Library Letterbook, Randolph, VT
- Onondaga County (NY) Public Library
- Cross' Mills Public Library Charlestown, RI
- New Gloucester (ME) Library
- Fuller Public LibraryHillsborough, NH