This is a brief guide to some sources on the history of Williams. The College provides a brief history, along with detailed biographies of its Presidents. See here for an overview of the life of Ephraim Williams. The Archives contain other material, see in particular this history of some of the most important people and events from the College's past.
This history of the sciences at Williams, the result of a collaborative effort among the students in History of Science 240 during the spring of 1992, is a fine example of what more could be done. See here for biographies of the members of the Williams class of 1863, created in conjunction with their 40th reunion.
Unfortunately, the most important book on the history of Williams --- "Mark Hopkins and The Log: Williams College, 1836-1872", by Emeritus Professor Frederick Rudolph '42 --- is not available on the web.