"We're obviously very appreciative of his generosity, and we're proud of his accomplishments as a mayor and a businessman," Belson said.
The donation, in the name of Bloomberg Philanthropies, is a departure from Bloomberg's usual practice of making donations in Medford anonymously, Belson said.
Bloomberg is a member of the Medford High School class of 1960, and his mother was a long-time Medford resident until her death at age 102 in 2011.
Charlotte Bloomberg was a regular patron of the Medford Public Library, and her son asked friends and family to make donations to the library in her memory. About $20,000 came in from various individuals and companies after her death, which is being used to have Brighton-based wood artist Michael DePierro overhaul the children's room, library assistant director Barbara Kerr said.
"It's really beautiful stuff," she said.
The work at the library began last year and is expected to be finished sometime this summer, Kerr said.