Jackson told 500 inmates gathered to meet him Thursday that people must stop thinking of prison as "free meals, medicine, heat and recreational activities." He urged them to vote and get tested for HIV.
Jackson's Chicago-based civil rights group, the Rainbow PUSH Coalition, says 25 inmates took HIV tests and several registered to vote.
Jackson also urged the inmates to "make better decisions."
Thursday marked Rainbow PUSH's 43rd anniversary. Jackson founded the organization on Christmas Day, 1971.