The work of the Harlem Children's Zone Project initially focused on a 24-block area in Central Harlem, from 116th Street to 123rd Street and from Fifth to Eighth Avenue. In 2004, the Zone expanded to 60 blocks, extending northward to 132nd Street and eastward to Madison Avenue. In 2007, the Zone expanded north to 143rd Street.

HCZ did a survey of the initial 24-block area and found that it had a a population of about 13,000 people, with 86% African-American and 12% Latino. There were approximately 3,000 children between the ages of zero and 18 in the original Zone with 61% of those children living in poverty. The unemployment rate was 19% and 41% of residents were below the poverty level.