Emerald (CDP), WisconsinEmerald is a census-designated place in St. Croix County, Wisconsin, United States. Emerald is located in the towns of Emerald and Glenwood, west-northwest of Glenwood City. As of the 2010 census, its population was 161.HistoryA post office called Emerald was established in 1872, and remained in operation until it was discontinued in 1985. The community took its name from the Town of Emerald.