Auto dealer license in South Dakoto to be introduced soon. Lincoln County is a county located in the U.S. state of South Dakota. In 2010 census, the population was 44,828 making it the third most populous county of the state. Its county seat and township is one of the top 10 fastest growing counties in the United States in terms of number of population growth, increasing the number of housing and many other factors. This is because the growth of Sioux Falls metropolitan area through the expansion of Sioux Falls, South and growth of its suburbs.