Most of the cases at the Pilgrim’s Pride food factory in Pool, near Redruth, were asymptomatic, the local public health team said.
An alert to the national test and trace service from a single member of staff led to 500 colleagues at the plant being tested.
The company says it has introduced additional measures and checks its compliance with Covid-19 controls on a daily basis.
A spokesperson for Pilgrim’s Pride said: “From the outset we have worked conscientiously to do all we can to protect our workforce and the local community.
“Our teams have been working extremely hard in collaboration with the local authority and public health to manage this challenging situation, and have bravely conducted themselves with professionalism and integrity as they continue to play their important role in maintaining the UK food supply chain.”
Interim director for Public Health for Cornwall council, Rachel Wigglesworth said: “Our team has been working tirelessly since the beginning of the pandemic, and have strengthened our local Covid-19 contact tracing approach to help detect cases early, prevent spread and support people to self-isolate.
“We’ve quickly identified and tested hundreds of people, and in finding people who weren’t displaying symptoms we have potentially stopped a much wider spread in our communities.
“We continue to closely monitor the situation and appreciate the cooperation of Pilgrim’s Pride and their employees.”
Coronavirus cases in the South West remain relatively low, despite spikes in other parts of the country.
In the seven days up to September 27, there was an infection rate of 31.5 per 100,000 people in Cornwall and Isles of Scilly, with 180 positive cases.
This was up from a prevalence of 20.1 per 100,00 people the week before, and 115 confirmed cases, according to calculations from the PA news agency.