Valadao thanked his supporters in a statement and said he was glad he had contributed to bringing about change in the Valley. Valadao had represented the district for three terms in Congress.
"Representing the Central Valley in Congress has been the honor of a lifetime. There are truly no words to express how grateful I am to my supporters, neighbors, and all those who make the Central Valley such an amazing place," the statement read.
Cox, who had declared victory over his opponent on November 28, said in a statement he had spoken to Valadao on the phone.
"I thanked Congressman Valadao and his family for their service to our country and our communities during the past six years. As the Congressman knows well, it is a great honor to be chosen to represent the people of the 21st District in the House of Representatives," he said.
Cox's statement said he had won by 862 votes -- a big difference from Election Night when Valadao led with more than 5,000 votes.
The Democratic Party now has picked up seven GOP-held seats in California and will begin the new session with a 46-7 advantage in the state's congressional delegation.
Here is the full statement by Valadao:
"Representing the Central Valley in Congress has been the honor of a lifetime. There are truly no words to express how grateful I am to my supporters, neighbors, and all those who make the Central Valley such an amazing place.
There is no doubt we are disappointed in the results of this election but, we can take pride in knowing that we brought about real, tangible change. We have reduced taxes for middle-class families, made huge strides in our battle for water, reformed the dairy industry for thousands of California farmers, improved access to healthcare for families throughout the Valley, and given our troops the support they deserve.
The Central Valley has always been and will always be my home and I am beyond grateful for the opportunity to have served the place I love."