Microsoft took over first place after closing yesterday at 2-point-9 trillion dollars, before devaluing slightly today to slump back down to second place.
Apple has two sites in Cork and employs around 6,000 people in the city.
The tech giant had held the title for three years and is back in first place now.
It comes as the US Customs Office is due to rule on a patent challenge affecting sales of the latest Apple Watch.
