By Amber Henshaw
BBC News, Khartoum
Ille Mary steps out of the back of the truck in South Sudan with her three small children and her few possessions caked from head-to-toe in red dust.
Ille Mary hopes the census will lead to changes in South Sudan
She made the long and difficult journey home to her village of Sinduru, 46km south of Juba, determined to be counted in a highly-political census which could pave the way for big change in Africa's biggest country.
The results will decide the sharing of power and wealth in her homeland.
"I am extremely happy to be back in my village. It looks the same as when I last saw it. It's a day that I have dreamt of for many years."
Ille has been living in a refugee camp in Uganda.
She was one of millions forced to flee from South Sudan during the civil war that ravaged the region for more than two decades.
She lost everything in the fighting - her father was killed, her mother disappeared in the bush and hasn't been seen since.
"I always wanted to come home because this is my motherland and now there is peace here. I wanted to come back for the census so I can be counted to help the south develop."
And many thousands have done the same - the authorities have noticed a surge of returnees ahead of the census.
Sudan's census was a key part of the north-south peace deal signed in 2005.
Under the Comprehensive Peace Agreement, the population count will be used to help determine power- and wealth-sharing.
The head of the United Nations Mission in South Sudan David Gressly said the country's first census since 1993 was highly significant.
"It's been a long time since the south has fully participated in a census and we don't really know the full impact of the war on the south," he said.
"This will give the government and all of us trying to support the reconstruction of the south clear information as to how things are progressing and where efforts need to be concentrated.
The census will be used to draw up constituency boundaries for national elections due next year and then a referendum on whether the south should secede, due in 2011.
The logistical and technical challenges of carrying out a census in Africa's largest country have been immense.
Many thousands of South Sudanese have returned for the census
The census has already been delayed three times - the north and south have struggled to agree on the questions among other things and there have been problems over finances.
Mapping the country ahead of the count has also been extremely difficult because large swathes of land have been inaccessible.
In the south there is also the problem of landmines.
Furthermore, there is a large nomadic population - some estimate about five million people.
The conflict in the western region of Darfur has also complicated the plans.
The census director for the north, Ibrahim Abbas, said there had been major logistical challenges.
"Some areas like Darfur, we had some security problems, some areas were not accessible and in the south we had some problems because some of the areas were mined."
After years of conflict, land mines remain a huge problem in South Sudan
Many Darfuris now living in makeshift camps scattered across the region forced to flee from their homes over the last five years of conflict are refusing to take part in the census.
They fear that the results will be used against them by the government.
Darfur's rebel groups are also united in their opposition to the population count.
The Justice and Equality Movement has threatened to attack anyone conducting the census to stop the poll from going ahead.
And it is not just the Darfuris who are suspicious.
From the outset, the census has shown the ongoing distrust between the two former enemies from north and south, who are now joined in a national coalition government, supposedly as partners in peace.
It hasn't helped that much of the Comprehensive Peace Agreement is still to be implemented - like demarcating the exact border between north and south and the status of the disputed oil-rich region of Abyei.
Just days before the census was due to start on 15 April, the government of South Sudan said it wanted to postpone the count until the end of the year.
Information Minister Gabriel Changson Chang said they were concerned about the number of southerners who still hadn't been repatriated.
Hundreds of thousands have returned but as many as two million southerners are still living in camps around the capital, Khartoum.
He said the southern government was worried that this would affect the results.
This month lobby group Justice Africa said: "If an accurate census were to reduce the figure for southerners, this would automatically reduce their representation in a post-2009 National Assembly and central government."
Some officials even accused Khartoum of deliberately stopping southerners returning - an allegation the north denies.
The government of South Sudan said it was also concerned that the question of ethnicity and religion had not been included in the census - the war was fought between the mainly Muslim, Arab north and the Christian and animist south.
After intense pressure from the international community, the south agreed the census could go ahead but the information minister said they would not be bound by the result.
This could mean that whatever the outcome of this census, the results are only going to spark further disputes down the road at a time when relations between north and south are already looking extremely shaky.