Happy Birthday to the Library of Congress, founded on April 24, 1800 when President John Adams signed the Congressional Act that created it. $5,000 was alotted for the collection. 740 books and 3 maps were ordered from England specifically to start the collection which was intended for use of the elected officials. Originally, it was housed in the US Capitol.
Ironically, during the War of 1812, the British burned the collection when they set fire to the Capitol Building. To reconstitute the Library, Thomas Jefferson sold his personal collection of 6,487 volumes to the nation. Nice move, Tom.
The Library currently hold 151,785,778 items - books, maps, "incunabula (books printed before 1500), monographs and serials, music, bound newspapers, pamphlets, technical reports, and other printed material, and 109,029,796 items in the nonclassified (special) collections".
for more information and history, see the wikipedia page on the Library of Congress