The survey, which takes place once every decade to gauge the demographics of the country and guide the future of public services, is due to close on Sunday.
Those who have not completed the census face prosecution and a fine of up to £1,000.
New figures from National Records of Scotland (NRS) show some 700,000 of the 2.7 million households have yet to submit their response.
Mr Robertson has urged Scots to take part.
“I want to thank the two million households who have already completed the census and met their legal responsibility,” he said.
“But as we enter the final week, many returns remain outstanding.
“For the census to be effective in delivering its many benefits for future public services, it is vital that we secure a higher response rate and one that reflects the diversity of our communities.
“Today we are calling on all of our communities and organisations to come together and to redouble their efforts to encourage participation.
“It’s absolutely essential that every householder in Scotland completes the census.”
The figures show the Glasgow City Council area has the lowest response rate, as of Monday morning, with just 65.5 per cent, compared to 82.2 per cent in Aberdeenshire.
NRS chief executive Paul Lowe said: “Census data is vital in informing decisions about services that affect us all.
“We have put in place a number of additional interventions to support those who have yet to complete a return. This includes a range of additional household reminders.”