The seat held by New South Wales Education Minister Adrian Piccoli is to be abolished at the next state election.
The new seat boundaries have been gazetted after a redistribution by the NSW Electoral Commission.
Mr Piccoli's seat of Murrumbidgee, which includes the towns of Griffith, Leeton, Junee and West Wyalong, is to be absorbed by the reconfigured seats of Burrinjuck and Murray-Darling.
The reconfiguration has been made to accommodate population growth in inner Sydney, with a new seat of Newtown to be created.
Mr Piccoli now has to decide which electorate to contest at the next state election.
"This is a stupid decision to turn three western NSW seats into two seats. It didn't need to happen," Mr Piccoli said.
"It's a matter of a discussion between my family and myself, because big electorates mean a lot of time away from your family."
His decision might be helped by Nationals colleague John Williams, who is currently the MP for Murray-Darling.
Mr Williams says he does not want to retire, but is considering whether to contest another neighbouring electorate, the reconfigured seat of Barwon, or move to the state's Upper House.
"Legislative Council is an option. We don't have anyone in western NSW at the moment," Mr Williams said.
"I've had a lot of colleagues have put a bit of pressure on me to take it on. There's quite a few things that could happen. I mean there's a lot of discussion going on about where people might move."
Barwon, currently held by Nationals MP Kevin Humphries, is to be extended westwards to the South Australian border.
Mr Humphries lives in Moree, which will no longer be part of his electorate, and it is not yet clear if he will renominate for Barwon or another seat.
The determination on the electorates is largely the same as draft proposals issued by the NSW Electoral Commission in June.