Lauren Castillo has illustrated many books for children, including Happy Like Soccer by Maribeth Boelts and Yard Sale by Eve Bunting. Lauren Castillo is also the author-illustrator of the Caldecott Honor Book Nana in the City. She lives in Harrisburg, Pennsylvania--the setting of Just Like Millie--with her two rescue dogs, who helped her acclimate to the city when she first moved there.