The number of Gypsy and traveller pitches in Cornwall is expected to rise sharply after a report said projections were far too low.
A government inspector said in May that Cornwall Council's assessment of 109 pitches for the next 15 years was not detailed enough.
Another survey by independent consultants said 318 sites were needed.
Edwina Hannaford, planning portfolio holder, said: "We did not delve deeply enough into the traveller lifestyle."
The latest census in 2011 showed there were about 640 Gypsies and Irish travellers in the county.
Cornwall currently has a total of 78 pitches for travellers and Gypsies according to the local authority, and was planning to supply another 109 by 2030.
Pitches figure 'ridiculous'
But another estimate of the need was ordered after an inspector of Cornwall's local plan criticised the assessment, highlighting "lack of engagement" with travellers.
The inspector also said overcrowded existing sites had not been taken into account.
The latest report by Southern Horizons with Plymouth University was produced after face-to-face consultation with Gypsies and travellers to assess their needs.
Councillor Hannaford said the report would become part of the local plan which outlines infrastructure needs in the county.
"We held our hands up. We did not understand the nature of travellers' movements and needs and their family make-up," she said.
"We want to do the right thing for this minority group."
But she admitted plans for more pitches would be a "challenge" because of opposition in some areas.
Caroline Dann of Traveller Space which campaigns for travellers in Cornwall, said: "The initial figure was ridiculous, we knew there were more people out there needing pitches.
"But you can't find out by sitting at a desk. The only way is to go out and find people and interview them."