Fire crews from Drogheda and Balbriggan attended the scene and brought the blaze under control, but not before significant damage was caused to parts of the building.
No injuries have been reported and the cause of the fire is not yet known.
The hotel has confirmed it will remain closed until further notice, with management working to contact customers who had bookings and upcoming events.
The Glenside is a well known venue locally, regularly hosting weddings and private functions.
Gardaí said they are assisting emergency services at the scene in Smithstown. In a statement they said: “The building has been evacuated and no injuries reported at this time. No further information.”
Local Sinn Féin councillor Debbie McCole said she was saddened by the news.
“My thoughts are with all the guests, staff, management and emergency services, dealing with the situation.
“I sincerely hope that everyone is safe and that no one has been injured. Incidents like this are distressing for all involved, especially the hardworking staff and management who will be facing a very difficult time.
“Thank you to our emergency services, especially Louth County Fire Service for their swift action.”
