 In 2005 West Des Moines annexed land in Warren County for the first time.Seeing the land to the south of Des Moines as extremely valuable, especially with the completion of a major "South-Belt Freeway" system, the cities of Norwalk and West Des Moines are actively competing for land in the northern part of Warren County.From 1990 to 2015, West Des Moines is the fastest growing city in Iowa according to land mass.