Defense attorney Cheryl Ramsey entered the plea for Blackmon during a hearing Tuesday that he did not attend.
Police arrested Blackmon during a traffic stop in Stillwater, Okla., on June 3. Authorities said a breath test showed his blood-alcohol content to be three times the legal limit.
Special Judge Michael Stano imposed a deferred sentence of one year, meaning Blackmon will serve no jail time if he fulfills the terms of his sentence. Blackmon was fined $500 and ordered to complete 50 hours of community service.
The Jaguars selected Blackmon fifth overall in April's draft. The former Oklahoma State star has apologized and says he'll abstain from alcohol use for now.