LaSalle-Peru, Ottawa, Morris and Rochelle sent a letter to Northern Illinois Big 12 president and Kaneland athletic director Peter Goff on Friday, informing the league of their decision to leave in 2019.
Those four schools will reportedly be joining Plano and Sandwich to form a new league.
"It's kind of the state we live in with the nature of conferences," Goff said. "We'll have to regroup and move on."
The exodus of the four schools leaves six teams in the NIB12 – DeKalb, Sycamore, Kaneland, Yorkville, Sterling and Geneseo.
Geneseo could be on the move, too. Sandwich Principal Thomas Sodaro confirmed in an email Friday that Geneseo, LaSalle-Peru, Morris, Ottawa and Rochelle have all been invited to join the Interstate Eight Conference for the 2019-20 school year.
"These schools will now work with their Boards of Education to make a decision in the near future," Sodaro said in the email.
Goff said with the conference just being informed of the split, there hasn't been time to work on plans for the future – whether it's trying to rebuild or split up.
"We don't know," Goff said. "We haven't all talked about anything but we plan to meet over the break and talk."
Goff said he's confident that the remaining teams will figure something out.
"I think we have a lot of great things to offer," Goff said. "The people that are left, our schools are competitive on the whole and I think you can see a lot of different things with different types of competition of a very high caliber.
"They needed to do what was right for their schools and communities, and we need to do what's right for our schools and our communities," Goff said. "Moving forward that's what we're going to do."
Plano, Sandwich and Westmont were left searching for a new conference affiliation when the eight other schools in the Interstate Eight Conference formally announced their decision in October to leave the league at the start of the 2019-2020 school year.
"We have to weigh it all together, we have to look at the big picture and what's best for us," Sandwich Athletic Director Timothy Gipe said in October.
Later in October Morris, Rochelle, Ottawa, LaSalle-Peru and Geneseo from the Northern Illinois Big 12, was invited to a meeting to discuss rebuilding the Interstate Eight.
One possible piece in any new scenario is Burlington Central, which was recently voted out of the Kishwaukee River Conference because of their expected increase in enrollment size. However, the school was offered an invitation to the Fox Valley Conference and is expected to have its school board vote on it in January.