Trek manufacturers only their top carbon fiber (CF) bikes in the USA (Emonda, Domane, Madone), but this relatively small part of Trek's total sales still makes it the largest bicycle manufacturer in the USA. Trek does this to protect it's secrets (intellectual property) of making light, strong frames from the Chinese, and also because you can evidently make a nice profit off USA-made $12,000 bikes. Most of Trek's CF bikes are made in Taiwan by Giant, the world's largest bike maker . Trek 520 is almost certainly made in Taiwan or China - Giant has factories there, but 520 may be made by someone else.