[Updated and comments opened.]

* Jason Plummer will run in the 12th Congressional District Republican primary. The 12th is currently represented by retiring Democratic Congressman Jerry Costello…

“I’m going to run in the 12th,” he told The State Journal-Register. “I made the decision this morning.”

Plummer had also considered running in the new 13th, which includes part of Springfield. But also living in that district and running for another term is U.S. Rep. Tim Johnson, R-Urbana.

Plummer, 29, said there’s plenty of need for good representation in the new 12th, where longtime incumbent U.S. Rep. Jerry Costello, D-Belleville, recently announced he’s not seeking another term.

The Illinois General Assembly, which is controlled by Democrats, drew new congressional maps this year following the 2010 Census. Plummer said his current residence is in the new 13th, not far from the 12th. He plans to relocate into the 12th, which takes in a chunk of southern Illinois that includes Belleville, East St. Louis, Alton and Carbondale.

* He could face Rep. Mike Bost in the Republican primary…

State Rep. Mike Bost, a Republican from Murphysboro, said Tuesday he’s considering a campaign for the 12th Congressional District. […]

Bost says this could be Republicans’ best shot at taking the seat. He expects to make a decision on running in the next three or four weeks.

Three other Republicans have already announced their candidacies in the race. They are Roger Cook of Belleville, Theresa Kormos of O’Fallon, and Teri Newman of Highland.

*** UPDATE *** Monroe County Republican Chairman Myron Neff claims Plummer is the NRCC’s guy…

Plummer has been polling in the downstate 12th and 13th CDs, for the past few weeks, and he’s been encouraged with the results. Neff says Plummer, who invested in his own 2010 bid for Lieutenant Governor with GOP candidate Bill Brady, will be funded.

“He’ll be able to raise the money,” Neff said, “and the NRCC is 100% behind him. This seat will be one of the top five for them.”