There's an IA birth record for a Mahlon W. WALKER b. 12-July-1887 in Irwin, Shelby Co, IA.His parents were Nicholas W. WALKER and Laura M. JOHNSON.
The 1910 census for Tulare, Spink Co, SD: WALKER, Nicholas W. age 55 b. TN wife Laura M. age 44 b. IA son Mahlon W. age 22 b. IA dau Blanche M. age 23 b. IA son Albert L. age 21 b. IA dau Myrtle N. age 19 b. IA son Francis A. age 17 b. IA son Ollie J. age 14 b. IA son Russell M. age 12 b. IA dau Cornelia E. age 9 b. IA dau Velma M. age 6 b. IA son Elmer L. age 3 b. IA son Lyle B. age 0 b. SD
According to the 1915 SD state census and his WWI draft card Mahlon's middle name was Willard.
In the 1900 census the family was in Greeley, Irwin Township, Shelby Co, IA.N.W. WALKER was b. Jan 1855 in TN, his father was born in NC, and his mother in TN.Wife Laura was born Dec 1865 in IA, both of her parents were born in TN.They were married 13 yrs and had 6 children, all of whom were still living (and match the names of the oldest 6 children on the 1910 census)
In 1920 Nicholas and Laura are in Garfield, Spink, SD with Ollie, Russell, Velma, Elmer and Lyle.In 1930 Nicholas is still in Garfield, widowed, with children Russell and Velma still at home.