Millennium Force design and development phases of Millennium Force took place over five years. The first rumors that a new record-breaking roller coaster would be built at Cedar Point, which included speculation about a ten inversion roller coaster from Bolliger & Mabillard and an Arrow Dynamics MegaLooper, began circulating in early 1998. A roller coaster from D. H. Morgan Manufacturing was also rumored. On July 2, 1999, Cedar Fair Entertainment Company filed a trademark for the name Millennium Force, which raised more speculation about what the ride would be like. About a week later, the first track pieces were seen at the
Six Flags Great Adventure at Six Flags Over Georgia and Six Flags Great America. In 2004, new harnesses were added to the Runaway Mine Train and the up-charge attraction erUPtion was added to the Boardwalk. In 2005, the park added the world's tallest coaster called Kingda Ka and also dismantled Viper. With the addition of Kingda Ka, the season pass holders entrance to the park was closed because Kingda Ka's footprint went right over it. A new children's play area called Balin's Jungleland was also added. In 2006, a wooden twister coaster called El Toro was added in the spot formerly occupied by Viper,