A CRJ200 cabin and cockpit filled with a white smoke immediately after takeoff. An emergency was declared; the flight returned to the departure airport and evacuated after clearing the runway.

Narrative

I was the First Officer operating a scheduled flight. The flight had total of three crew members and four passengers on board. After push back; we taxied out to the de-ice pad for application of type one and four deice fluids. After the completion of the deice procedure we taxied to Runway 4. Shortly after departure; at around 200-300 FT the cockpit started to fill out with white smoke that came from the rear air vents in the cockpit. Both the Captain and I put on our Oxygen masks. The Captain; who was flying; took over the radios while I completed performing the QRH emergency checklist for smoke removal. After the completion of the emergency checklist; there was no visible smoke in the cockpit. The Captain declared an emergency; Departure was notified about the nature of the emergency and that we asked for vectors and a return to land. Flight crew maintained communication with Dispatch via ACARS. I notified the Flight Attendant about the situation in the cockpit and that we are returning. The Flight Attendant informed me that visible smoke was present at the cabin shortly after takeoff. Flight got vectors and landed on Runway 4. Shortly after clearing the runway; both Captain and I removed our oxygen masks and still smelled an odd odor. Flight crew decided to perform immediate actions and evacuated the airplane on the taxiway. All crew and passengers were unharmed and the incident ended with no injuries. At this point of time; the reason for the smoke in the cockpit and cabin is unknown. The airplane was removed from service and is being checked by maintenance personnel.