It was followed by the Philippines with 950,000 and Vietnam with 779,000, according to data from tourism ministries across the region.
Singapore came in fourth with 763,000 American arrivals, while Malaysia recorded over 418,000.
Thailand last year increased visa-free stay for citizens of 93 countries and territories including the U.S., up from the previous 57, allowing visitors to stay for up to 60 days.
It also introduced its Destination Thailand Visa that allows digital nomads, freelancers and tourists interested in activities like cooking and martial arts to stay for up to 180 days at a time over five years.
Vietnam has recently emerged as a favorite destination of American tourists.
The U.S. topped the list of 10 countries with the highest number of searches for Vietnam tourism in early 2025, followed by Australia and India, according to Google's Destination Insights.