They said the increase of about 1,000 would help to generate up to Â£3m for the local economy.
More than 300 acts have been lined up to appear over the four-day programme on the Raehills Estate near Beattock from 8 to 11 June.
The list of headliners includes Gogol Bordello, Boney M., Cat Power, So Solid Crew, 2ManyDJs and Admiral Fallow.
Founder Adam Curtis said that although attendances were increasing he did not anticipate the event getting  much bigger.
"We have got record numbers expected down in the field so it has crept from 8,000 to 9,000," he said.
"We are hoping for next year, for the 10-year anniversary, we should be at 10,000 people.
"The total number we are pushing to with the festival will probably stay under 15,000 so we are most of the way there."
The Eden Festival's value to the area's economy and visitor sector has been recognised by Dumfries and Galloway Council which this year provided the organisers with an Â£18,000 grant as part of its major events strategy.
Council events champion Adam Wilson said that was "pumping millions" into the region.
"For Moffat and Lockerbie and Dumfries, tourism is really important and there are a lot of people feel that actually the council isn't doing enough for the tourism industry," he said.
"I think it is a very significant strategy that we have - it is very important and it is working."
Organisers of the Eden Festival have confirmed they are increasing capacity to a record 9,000 this year.