The group, who left the Mabia camp in southern Sudan two months ago, were seeking to return to homes they fled in 2001 after the southern province of Bahr el-Ghazal was taken over by government forces, said Jemini Pandya, a spokeswoman for the International Organization for Migration.
Under the terms of a January peace deal between Khartoum and rebel groups, government forces were expected to relinquish control of the region.
"They are making steady progress," Pandya said, adding that the next 25 miles "will be the most difficult, where they will have to travel through dense forest and cross a river."
"Then they will reach the Savannah, where it will be easier."
The group already has walked 124 miles over difficult terrain, including forests and swamps, but they still are weeks away from their destination, she said.
Sudan's 21-year war pitted the Arab Muslim-dominated government in Khartoum against rebels fighting for greater autonomy and a larger share of the country's wealth in the largely African animist and Christian south.
More than 2 million people died, mainly from war-induced famine and disease, and at least twice as many fled their homes. Southern Sudan's conflict was separate from one in the country's western Darfur region.
Pandya said IOM staff, including a doctor, were accompanying the group on their trek home and that the agency was using trucks to carry the most vulnerable, including pregnant women, the elderly, blind and handicapped.
IOM said many began the march with illnesses such as malaria and acute respiratory infections. There also has been a slight increase in the number of diarrhea cases since they left Mabia.