Police closed the highway's eastbound lanes for an hour after the incident.
The preliminary investigation shows a semitrailer truck heading east with a load of sand, just east of Jordan Lake Road, struck the man.
Police said the victim, a 24-year-old Dimondale man, was taken to Spectrum Butterworth Hospital in Grand Rapids in critical condition.
Police are looking into whether alcohol may have been a factor on the part of the pedestrian.
Anyone who may have seen the man walking along the highway before the crash is asked to call the Ionia County Sheriff's Office at 616-527-5737 or Silent Observer at 616-527-0107.