The People's Free Library of South Carolina that was established in 1903 in Chester County, South Carolina may be able to give the bookmobile a challenge to the "first bookmobile in the United States" title.
According to the University of South Carolina's history of public libraries in the state: "The People's Free Library brought limited services to the surrounding countryside by a mule drawn wagon carrying wooden boxes of books." http://www.libsci.sc.edu/histories/vts/vts09.html
It looks like more research needs to be done to verify dates--there are probably other early bookmobile services around the country as well that need to be better documented.
According to the University of South Carolina's history of public libraries in the state: "The People's Free Library brought limited services to the surrounding countryside by a mule drawn wagon carrying wooden boxes of books." http://www.libsci.sc.edu/histories/vts/vts09.html
It looks like more research needs to be done to verify dates--there are probably other early bookmobile services around the country as well that need to be better documented.