The injured man was riding a motorcycle.
Route 75 near Ed McClain Road in Monrovia was closed for about two hours Friday afternoon following a three-vehicle crash.
State Police say Timothy Hamilton, 37, of Ijamsville, was riding his motorcycle along Route 75 at a "speed greater than reasonable and prudent" according to a news release from the local barrack. Hamilton's bike crossed the center line of the roadway, and struck a pickup truck head-on. The pickup was puling a 15-foot box trailer.
Hamilton was thrown from his motorcycle.
The State Police medivac helicopter flew Hamilton to Shock Trauma in Baltimore. As of Friday night, his condition was listed as critical.
The driver of the pickup truck, Sarah Horton, 33, of Dickerson, and her passenger, an eight-year-old child, were not hurt.
The investigation into this crash is continuing.