Christy Park, according to the city website, is comprised of 16.1 acres of park land, established in 1910. There are no official boundaries listed on that website, so I can only assume that Christy Park and Joseph Leisure Parks are one in the same. There is actually a band of parks that start at Kingshighway and Christy and head south and east toward the River Des Peres, following the Great Rivers Greenway Trail starting near Christy and Holly Hills Boulevards.
It's an oddly shaped neighborhood that does not include Carondelet Park nor the Loughborough Commons shopping center. I always thought the River Des Peres was the dividing line between the city and the county, but the map above from the city website shows the city limits extending south of River Des Peres to Weber road. The neighborhood has some areas that are typical of south city, a la Holly Hills, Princeton Heights, Southampton, etc. Other parts of the neighborhood are more suburban with cul-de-sacs and no sidewalks, etc.