It occurred over the weekend of Friday 3 August to Monday 6 August 2012, from the Romanby Water Treatment Plant on Wooden Hill Lane in Romanby.
The thieves stole a laptop computer, a digital camera, a mobile phone and several hundred pounds sterling.
PC Nick Hill, of Northallerton Safer Neighbourhood Team, said:
If you can help with this investigation please contact the police or Crimestoppers straight away.
Anyone who can assist with this investigation is asked to contact Northallerton police on 101, select option 2 and ask for Nick Hill.
Or call Crimestoppers anonymously on 0800 555 111 quoting reference number 12120128804.