Central Park is 37 times larger than Millennium Park.
Area: 3 km2 calculated
Central Park is an urban park in the New York City borough of Manhattan. It was initially opened in 1857, on 778 acres of city-owned land. In 1858, Frederick Law Olmsted and Calvert Vaux won a design competition to improve and expand the park with a plan they titled the Greensward Plan. Wikipedia
Area: 0 km2 calculated
Millennium Park is a public park located in the Loop community area of Chicago in Illinois, US, and originally intended to celebrate the millennium. It is a prominent civic center near the city's Lake Michigan shoreline that covers a 24.5-acre section of northwestern Grant Park. Wikipedia