Crossword puzzle clue "in a worn state"

It may not be worn when it's worn

A waistcoat worn in summer, compared to one worn in winter?

Illinois, Indiana, Iowa, Michigan, Michigan State, Minnesota, Northwestern, Ohio State, Penn State, Purdue and Wisconsin

In a worn state

Article of tropical apparel ... whose start is a state nickname for the state indicated by the circled squares

Unlikely state of a state?

Secretariat's mother, for one ... whose start is a state nickname for the state indicated by the circled squares

State made up of two state postal abbreviations