In the video, which parked outrage on social media, the dog is in a crate on that trailer, which is attached to an SUV.
The man who took the video says he spotted the dog while traveling on eastbound I-80/I-94 near Calumet Avenue in Hammond on Tuesday morning.
He says he couldn't believe what he was seeing, describing the dog as "scared" and "shivering."
Officers were able to track down the dog and a person they have identified as a suspect.
The dog is safe and will receive treatment, ISP said. K-9 handlers have been working with the dog to make him more comfortable.
Investigators sent the case to the Lake County, Indiana prosecutor's office. They will review the evidence and decide on any charges.
ISP said further information is expected to be released on Thursday.