Hello. I do not know exactly when but for a number of years now, FN has supervised assembling operations in Portugal due to labor costs in Belgium. Reportedly, a misreading of US importation laws resulted in Browning-marked Hi Powers bearing the "Made in Belgium/Assembled in Portugal" markings where the FN-marked Hi Powers did not...even though they too were assembled there and have been for something in the neighborhood of a decade now.
No FN/Browning Hi Powers have been manufactured in the US, ever. Some FN firearms definitely are such as the FNP/FNX line of handguns and our military's M16's and so forth but not the Hi Power. They are made in Herstal, Belgium.
Here is a somewhat related article that might be of interest:
hi-powers--handguns: "Portuguese Hi Powers"
Best to you and yours.