Agency or state?

Hi, there. I am interested in becoming a foster parent, but am having much difficulty deciding how to go about it. I called an agency about a week and a half ago, who said that their duty was to hook people up with foster agencies in the area, and I've heard nothing back despite repeated follow up calls thanks by me. I live in St. Charles city and would appreciate advice. Should I go through the city, or through an agency, what is the difference, and which agencies are good? Thank you so much. :thanks: