The census is conducted every 10 years
MPs have rejected a bid to allow people to list their nationality as "Cornish" on the 2011 census.
Cornwall North's MP Dan Rogerson had put forward the proposal as MPs debated the Draft Census Order 2009 for England and Wales.
A Facebook campaign Cornish Tickbox for the 2011 Census has been backed by Mr Rogerson and more than 3,000 people.
But as MPs rejected it by 261 votes to 49, they approved questions the Tories say amount to "bedroom snooping".
The government says the issue of Cornish language and identity was "considered" by the Office for National Statistics but was "not included in the proposals for the 2011 census".
But Lib Dem MP Mr Rogerson had attempted to introduce it as an amendment to the Draft Census Order 2009 for England and Wales.
There will be no tick box for people to put their nationality as "Cornish" on the next census, set to be carried out on 27 March 2011.
Instead, they will have to tick "other" and then write in their response. Critics say many people will not realise they can do this, and will select English, Scottish, Welsh, Northern Irish or British.
MPs voted by 298 to 127 to approve the new census questions, which had previously been criticised by the Conservatives as "intrusive".
Questions will include the number of bedrooms in a home and the name, age and sex of any overnight visitors.
The statistics watchdog rejected the Tory attack and said they would help show overcrowding and give a more accurate picture of the population.
The census, which is conducted every 10 years, is designed to give an accurate snapshot of demographic and social changes in the UK.