Simplify the following text for a Grade 13 native English-speaking person.
Original: The UK 2001 census was organised by the Office for National Statistics ( ONS ) in England and Wales , the General Register Office for Scotland ( GROS ) and the Northern Ireland Statistics and Research Agency ( NISRA ) .
Simplified: United Kingdom Census 2001 was started by the Office for National Statistics in England and Wales , the General Register Office for Scotland and the Northern Ireland Statistics and Research Agency .