The Frenchman Bay Conservancy has been working to revitalize the area since 2013.
Over the past year, members have cleaned up some of the land, removed a few small buildings and built a new headquarters.
The kickoff included food vendors, live music and family games.
"We do this with membership support and we're so grateful for our members because they provide us the financial assistance that we need in order to be able to conserve land," said Aaron Dority, the conservancy's executive director.
Dority said Monday's celebration was a way to give back to those who have supported the effort.
The preserve has more than 8,000 acres and 25 miles of trails. It is open for the public to enjoy.