The park was originally outside the city limits of Champaign, and was part of a planned real estate development by Fred Hessel called Highland Place, and was initially supposed to have a lagoon for boating and fishing. That obviously never happened, but Hessel Park definitely became and still is a favorite recreational spot in the community.
You can read more about Fred Hessel on the Champaign County History Museum website, including his plan for a "University City" that would've been a separate entity from Champaign and Urbana.
Top photo from Champaign County History Museum. Current photo from Champaign Park District website.