As demonstrators marched along County Route 533, a deer ran from the high school property into the marchers, according to police.
A woman, 69, was transported to an area hospital after receiving a "serious head injury."
On Friday night, she was listed in intensive care but her condition "improved" as of Saturday, according to police.
"We continue to pray for her complete recovery," police tweeted.
Two other people who were injured when the deer ran into the crowd were treated at the scene. Officers working with the event provided medical aid until emergency medical services arrived.
Two people were treated for heat-related issues at the march and rally, FOX5 reported.
The peaceful demonstration drew some 1,000 people, with attendees holding signs that read, "We all bleed the same color," and "Stop killing us," according to mycentraljersey.com.