"Scouting locations for Cybertruck Gigafactory. Will be central USA," Musk wrote. "Model Y production for east coast too."
Musk unveiled the truck, Tesla's sixth model, in November at a company event in Los Angeles, and said it will start at $39,900. The truck, shaped like a large metallic trapezoid, will be competing against American-made trucks like the Ford F Series and General Motors' Chevrolet Silverado.
The Model Y, announced in March, will seat up to seven and could start deliveries in the first quarter of this year, according to a December report from Deutsche Bank. Should Tesla build Model Ys in the new factory, the vehicle will be manufactured in four places -- China, Germany and Fremont, California, are the others.
Investors have grown accustomed to Musk making lofty promises that either end up being premature or don't come true at all, such as a 2016 promise to have a Tesla drive itself across the U.S. by the end of 2017, and multiple predictions for Model 3 production numbers that the company did not reach.
He's also hinted at other facilities in the U.S.
CNBC's Lora Kolodny contributed to this report.