Wilder De Ayr Foster (January 8, 1819 – September 20, 1873) was a politician from the U.S. state of Michigan.

Foster was born in Orange County, New York where he attended the common schools.

He was city treasurer and member of the board of aldermen and then became Mayor of Grand Rapids in 1854.

In a special election on April 4, 1871, Foster was elected as a Republican from Michigan's 4th congressional district to the 42nd United States Congress to fill the vacancy caused by the resignation of Thomas White Ferry.

(Foster defeated Ferry's brother William, who ran as the Democratic nominee.)