Who is in charge of homelessness in the USA?

Homelessness is a blight, a problem for the state and a problem for those who suffer from it. I want to know who to talk to about this topic; I want to send letters/emails about my ideas for homelessnes to the person/people in charge. At the same time, if there are any resources I should use to learn more about what is currently being done to address homelessness, let me know where to look.