I found hundreds of these along a trail in north-western Ohio. The one pictured is about 2 inches long, but there were some that were very small, only 3/4 of an inch or so.
our caterpillar is the orange-tipped oakworm moth caterpillar.
This caterpillar is found widespread in eastern United States and parts of southern Canada.
According to bugguide.net, (the most up-to-date source of scientific names of insects) this insect may actually be three different species that can only be separated in the larvae stage. ” Larval characteristics may give one an identification of the regional forms (Anisota senatoria, or peigleri, or finlaysoni), which may be separate species, or a cline (regional forms) ”
With that said…the adult moths do not feed. The caterpillars feed on oaks as the name suggests :-), (tho some have been found to feed on water chestnuts and on laurel in the south). The larvae stay together in the early stages but spread out as they get larger. Populations can get to be a pest problem. But as you noted, it was in a public park so there is no need to worry about control.