Clement Clarke Moore (July 15, 1779 – July 10, 1863) was an American professor of Oriental and Greek literature at Columbia College, now Columbia University. He donated land from his family estate for the foundation of the General Theological Seminary, where he was a professor of Biblical learning and compiled a two-volume Hebrew dictionary. He is generally considered to be the author of the yuletide poem "A Visit from St. Nicholas", which later became famous as "'Twas the Night Before Christmas" .
This park was the site of Moore's estate Chelsea, which was named after the district of the same name in London, and which lent its name to the present NYC neighborhood. It's a pretty little park, but don't even think about using the swings unless you're twelve or under. They're strict about that, in that self-righteous Manhattan way! More information is available about the man and the park at the related web page listed above.
A tip of the hat to Caitlin535, whom I discovered had found the cache before I'd learned it was published!