Declan, I've checked several sources and cannot find "people" listed as a collective noun. I did find this definition:

n. pl. people

Humans considered as a group or in indefinite numbers: People were dancing in the street. I met all sorts of people.

A body of persons living in the same country under one national government; a nationality.

pl. peo·ples A body of persons sharing a common religion, culture, language, or inherited condition of life.

Persons with regard to their residence, class, profession, or group: city people.