I know of someone taking care of an older person who's getting paid under the table and stealing money and prescription pills. Who do I contact?

You have no first hand evidence, just hearsay. You cannot file a credible police report, and you could be sued for defamation. Keep your ears open and your mouth shut unless you have all the facts.

Tell the police. Call APS...they can check their system to see if they are familiar with her on other cases. Does the crook's family know she's doing this? Would they care or try to intervene? Does the crook have minor children at home? Call CPS about her drugs use and sales. Is she on welfare, food stamps or Medicaid? Call the welfare department.