A folk game called monopoly was played extensively all over the Eastern half of the United States between about 1910 to 1936.
Players personalised the game with their local street names. It was a derivative of "The Landlord's Game" by Lizzie Magie, which was patented by her in 1904. In all likelyhood, it was also Magie who changed this game into monopoly.
(Also see much more on Thomas Forsyth's site "Early Game History - 1903 to 1936").
The game now sold as Monopoly was actually invented in and around the Atlantic City Friends School. The invention was a cooperative effort centered on Ruth Hoskins and Jesse Raiford, Cyril and Ruth Harvey. (See "The Billion Dollar Monopoly Swindle", by Ralph Anspach, 1sted.page 190, 2nd ed.page 296).
The game was taught to Charles Darrow by the Quakers and he commercialized it with 5,000 sets, claiming falsely he had invented it. He then licensed it to Parker Brothers in 1934.
Ralph Anspach is now (1999) marketing a replica of the game invented by the Quakers under the name "The ORIGINAL monopoly game".