Checks in Sheffield found 374 young adults watching television in Sheffield without a licence over the last year.
TV Licensing carried out the checks and found many culprits were students.
It warned that those caught without a licence could face prosecution and a fine of up to £1,000.
Matthew Thompson, of TV Licensing, said: “On average, students own three devices capable of streaming live TV so it is important they understand the law when it comes TV and devices.
“Watching live TV on any device is illegal without a TV licence, and could result in prosecution and fine of up to £1,000.
“If you’re a student and you are worried about paying for a TV licence, get in touch. We know some people struggle to pay which is why we have many payment options.”