George S. Parker published the game 'Banking' in 1883. Lizzie Magie patented The Landlord's Game in 1904 which was published in 1910 by The Economic Game Company. Lizzie Magie gained an additional patent for the changes she had made to her game. A woman named Ruth Hoskins changed the street names om the game to street names within Atlantic City. In 1933, Charles Darrow manufactured five thousand Monopoly games and was issued a patent in 1935, which he assigned to Parker Brothers. Parker Brothers began marketing the game that same year. All Monopoly games sold prior to 1949 carry the patents of Lizzie Magie and Charles Darrow.
It is estimated that over five hundred million people have played Monopoly since it's creation in 1935.
What's it worth? Take a look at this Monopoly price guide: sold listings for a value indication.