Brussels sprouts were first grown in an area near what is now known as Brussels, Belgium, which is why we refer to them as Brussels sprouts. They may have been grown there as early as the 13th century, but definitely by the 16th century. They later became popular in the Netherlands, which is now the largest producer of Brussels sprouts. Many people refer to them as “Brussel sprouts”, dropping the “s” in Brussels, but that is incorrect. The grammar police thank you for your attention to this matter.