The 25-year-old went missing in August and his body was found last month in the Illinois River in LaSalle County.
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His mother, Carmen Bolden Day, spoke at the service.
If you had met him, you would have liked him," she said. "thank you for realizing Jelani was important. Not just us, but he was important to everybody."
Day's cause of death has not been released. Police are still investigating the case, along with the FBI.
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There will be a celebration of life in Day's hometown of Danville Saturday.