[3] In December 1845 a group of civic leaders and philanthropists joined to establish a membership library with the intent of creating a place "where young men could pass their evenings agreeably and profitably, and thus be protected from the temptations to folly that ever beset unguarded youth in large towns.

The St. Louis Mercantile Library, with a reading room, meeting rooms, book stacks, and the largest auditorium in the city, became a primary hub of cultural and intellectual interchange in the city in the years preceding commonplace public and academic libraries.

A series of lectures were held in the auditorium, with noted speakers including Mark Twain, Carl Schurz, Ralph Waldo Emerson and Oscar Wilde.

The first session of the Missouri Constitutional Convention in 1861 met in the library voting to stay in the Union at the beginning of the American Civil War.

[2] The Mercantile Library historically collected materials to reflect the industrial history of St. Louis and the surrounding region.

[5] In 1985, the library established a formal waterways collection named after Herman T. Pott, a prominent river industry executive.

[6] The newspaper photo morgue and clipping files of the St. Louis Globe-Democrat, established in 1854, moved to the library.