Talk about imposing: the ceremonial stone stair leading to bronze gates and carved doors; the frieze of inspiring names and the vaulted hall that seems the very definition of hallowed. And the books, bound portals opening to anywhere imaginable, available to all comers.

In cities across the nation, the central public library came into being when the country was young and striving to impress. Charles F. McKim's Italianate palazzo-style library opened on Boston's Copley Plaza in 1895; in 1921, Renaissance austerity suited Detroit's...