About 170 steers, along with entertainers, sauntered and tromped down Main Street in downtown Pleasanton beginning at 10:30 a.m.
Organizers said it is the last opportunity for people to see a live cattle drive through an urban area.
After three years the fair decided it was discontinuing the cattle drive.
"We planned for the last cattle driver. We're trying to think how can we create something that celebrates who we are, but is bigger and better," said Angel Moore, an Alameda County Fair spokeswoman.
While the cows trodded along, the pigs were flying by at one of the bigest attractions at the fair—the pig races.
Some 450,000 people are expected to attend the county fair over the next 18 days.
"I come every year. I grew up coming to the fair sincer I was little," said Danae Rogers of Walnut Creek.
"It's cheap entertainment. It's kind of a tradition. We come every year," said Shawn Worth of Livermore.
The fair has a new ride this year called Mega Flip.
"[It was] like the floor went down. It was so fun. Hen it was spinning and everyone went ahhh," said 10 year-old Malia Rubino.
The fair runs through July 7, with live music every night.
Organizers are glad the fair didn't open last wekend when temperatures broke 100 degrees.
The weather Friday was about 20 degrees cooler.
The event is free to the public.