The Japanese automakers may invest a total of 150 billion yen to 200 billion yen ($1.36 billion to $1.81 billion) in the facility, which would possibly start operating in the early 2020s and produce 300,000 cars a year, mainly midsize and large models.
Mazda does not have a plant in the U.S., while Toyota produces about half of its cars there -- a smaller ratio than Honda Motor, among other rivals.
One likely aim of such a move would be to fall in step with U.S. President Donald Trump's protectionist policies. The project would also lower currency risk while helping the companies better meet local needs.
The partners are expected to initially focus on making popular SUV models. But because SUV demand is susceptible to oil prices and other factors, the automakers will take measures enabling them to easily switch production to other models.
Mazda's sole production base in North America is in Mexico. The SUVs it sells in the U.S. are imported from Japan.