Wingecarribee Shire Council's website at the time of writing offers absolutely no information about this park apart from its location. However, The Bushies have provided info in their Found log: This park was named after a Jim Cosgrove who played a major part in creating Moss Vale Leighton gardens and many other parks in the Moss Vale area in the 1960- 1990 era. He was the first full time gardener employed by the Wingecarribee Shire Council so they decided to honour him with a park. Hence "Cosgrove Park". He still has two of his children living in the area. If you Google Jim Cosgrove it may tell you more.
Anyway, I stopped here on a whim with the kids to read the sign board - I'm a sucker for an information board or a plaque. Given it was a beautiful, sunny winter Saturday afternoon and nobody was around, I assume this park doesn't get much use. It seemed like a good spot to place another cache in the run-up to the "31 Days of Caching" in August 2013, giving the locals another find without having to go too far afield.
** Congrats to cnschulz for FTF! **