Authorities seized the unemployed man's computer and are scouring it to identify and contact potential participants in the mass suicide planned for 14 February.
"They are doing welfare checks on all of them," Klamath County Sheriff Captain Chris Montenaro said.
Gerald Krien, 26, was charged with solicitation to commit attempted aggravated murder. He could face 10 to 30 years in prison if convicted.
Participants in the planned group suicide appeared to be people "not happy with that date of 14 February – observed as Valentine's Day - and not happy with their own personal lives," Montenaro said.
The police were tipped off by a Canadian woman who learned that one mother was allegedly planning to kill her two children and take her own life.
The chatroom was designed for people interested in suicide, Montenaro said.
Krien lives with his parents in the southern Oregon town of Klamath Falls. He has had no prior contact with local law enforcement and is being held on $100,000 bail.