The First Minister said officials were confident the once-in-a-decade survey of the population would provide "high-quality" data.
Critics have accused the Scottish Government of overseeing a shambolic and chaotic process.
As of Tuesday morning, 86.9 per cent of households in Scotland had returned the form.
In England and Wales, 97 per cent of households completed the census, which took place last year.
Scotland’s census deadline was extended last month to May 31.
However, updated advice says households can avoid a possible fine if they complete the form by June 12.
During First Minister’s Questions, Labour MSP Sarah Boyack asked whether the census had been a "credible exercise".
Ms Sturgeon sparked laughter when she replied: "Yes, it has."
She said the National Records of Scotland (NRS) was "confident that the national return rate and the coverage across the country, coupled with the normal, planned, post-collection quality control and assurance work, will provide credible, high-quality outputs".
Speaking afterwards, Ms Boyack said: “The First Minister’s response to this shambles is about as credible as this census data.
“It is farcical to see Nicola Sturgeon insist everything is going to plan while her Government scramble to push the deadline back for a second time this year.”
Earlier, Tory MSP Donald Cameron MSP said: “This whole process has descended into chaos – and it’s a shambles entirely of the SNP Government’s making.
“We warned them of the perils of not running the census in sync with the rest of the UK last year.”