CENSUS investigators are taking to the streets of Doncaster targeting households who have still not filled out the questionnaire.
People who refuse to fill in the Census face up to £1,000 fine.
Non-compliance staff will begin conducting interviews under caution with householders who are refusing to fill in their form.
Since Census Day on March 27, letters and cards reminding people that returning the questionnaire - which takes place every decade - is required by law have been posted to households where there is no record of a form having been returned.
Census forms can still be returned in the pre-paid envelope or online via www.census.gov.uk