A South Australian country show has celebrated its 100th birthday with great weather and a huge crowd.

The Yallunda Flat Showground is on the way to Cummins on the Eyre Peninsula.

The day also celebrated the official opening of the new shearing complex, which was built from donations from local farmers.

Show president Jim Cabot says country shows couldn't run without help from the community.

"What we have achieved in building this complex here is unbelievable, because we have had so much help from our community - Cummins, Tumby Bay, the whole area.

"We didn't have any money, so we asked for donations and people in the district had old shearing sheds to donate and there was lots of them, so we dismantled them all except one, managed to put it all together and come up with something that no one has ever seen before."

President of the Agricultural Societies Council of South Australia, Keith Collier, came along to the celebrations and was very impressed by not only the show, but the new shearing shed.

"I am just absolutely amazed with what a small community can do when volunteers get together.

"It's just a classic example of the great sprit that the community has to build a complex like this and I would say it is the best shearing shed I have seen at a country show."