The first bookmobile in the United States was started by Librarian Mary Titcomb in 1905you can read more of the details at
WHILBR and
PBS.
The first Bookmobile in Vermont started in 1922. Service was suspended in 1974 for almost 20 years but was later resurrected.
Here is an overview from 2001 and if you want to read more, check at your local library for Vermont Life MagazineBookmobiles are Back!Volume 128, Spring 2004 by Ann Marie Giroux.