The census is scheduled for Tuesday, but the federal government says if you know where you'll be on the night, there's no need to wait.

"Early completion will help ensure a successful census," Assistant Treasurer Michael Sukkar said on Wednesday.

The first households started getting letters about how to fill out their online census forms last week, with 1,023,561 already lodged.

The Australian Bureau of Statistics expects about 75 per cent of people will complete the August 10 census online.

The predominantly online population count comes five years after the ABS's first attempt to conduct an online census in 2016.

That count was largely declared a failure after the census website was hit by cyber-attacks that took the system offline for about 40 hours.

Meanwhile, Minister for Veterans' Affairs and Defence Personnel Andrew Gee has encouraged serving and former Defence Force members to disclose their service on their census forms.

"Presently we do not have comprehensive demographic information about our veteran community, including simply knowing the number of veterans living in Australia," he said.

The information will help the government get services to veterans and their families in the places where they're needed most.

Australian Associated Press