For the first time in five years, Australians will curl up with their Census forms tonight to give the Australian Bureau of Statistics (ABS) a snapshot of what the country looks like at this point in time.

The Census is used by government when planning infrastructure, community services and facilities such as schools, hospitals and roads.

Federal funding arrangements to the states and territories, including allocation of $45 billion in GST revenue, are also based on Census information, according to the ABS.

And this isn't just any old Census, tonight marks 100 years of Census.

In the first Census of 1911, Australia's population was counted as less than 4.5 million, with many collectors using horses to deliver and collect information.

A lot has changed since that time; Australia has a population of around 22.5 million with forms being filled out in 9.8 million households. It will cost around $440 million or about $19 each, with the largest single cost being $159 million in salaries paid to around 43,000 people to help deliver and collect the Census forms.

You can even choose to fill out an eCensus form online. Now that's something the computers of 1911 couldn't offer.