Charles cook/ Nannie Darcus ?

I am starting my COOK family research and my Grandfather, who I never met, was Named Charles Cook.He was married once before my grandmther, Nannie Darcus, I think Whiteaker, and had three children by his first wife who died.My grandmother raised his children and had five more.The first child of Nannie and Charles was born in South Dakota in 1919.There is an Unckle Frank and Aunt Annie my mother used to talk about but I am not sure if they were grampas family or grandmas.They would have been in South Dakota or Minnesota.Thank You