Reports are also indicating that Mercer was a student at the college.
According to Douglas County Sheriff John Hanlin, officers engaged the 26 year old Mercer and he is now deceased.
"They located the shooter in one of the buildings. Officers engaged that suspect. There was an exchange of gunfire. The shooter threat was neutralized.
"Officers continued to sweep the campus looking for other threats. We have confirmed that there is confirmed injuries and confirmed fatalities," Hanlin said.
Police investigators are looking at social media postings they believe were made by the suspect. On Wednesday night, the shooter appears to have had a conversation with others online about his intentions.
In a news release, Oregon Gov. Kate Brown said:
"Today is heartbreaking for Umpqua Community College, the greater Roseburg community, and all of Oregon.
"My heart is heavy as details of today's shooting become available. While it is still too early to know all of the facts, the effects of an incident such as this one are long-lasting.
"Please join me in keeping the victims and their families, as well as first responders, in your thoughts."