I've bought a bunch of Wilton 400 series forged clamps in the past year, all have been made in China. The quality is as good as any.
All Wilton cast clamps I've seen recently have been MIC, as well. I never have used cast clamps, but I'm very suspicious of Chinese castings.
So, if Wilton is making any clamps in the USA these days, it would be above the 400 series. I haven't seen any recent production of those.