Library Director Janet Campbell plans to retire next month after 37 years at the Mansfield Public Library. Campbell started out in 1976 as a youth librarian and continued in that role until she was appointed library director in 2001. “My husband retired eight years ago, and I decided it was time to join him,’’ said the 62-year-old Wareham resident. “The town has been tremendously supportive all these years, and I’m going on a happy note. I know I’m going to miss it here terribly.” Campbell said her exact date of retirement will be sometime in late March. Those who want to say goodbye to Campbell can do so at a reception from 4 to 5 p.m. on March 6 at the library. The Board of Library Trustees has not appointed a replacement for Campbell, who said a new director will probably be named in late April or early May.