Deloitte has said all of Poundworld's stores will likely close by August 10, affecting 2,339 staff.
The stores in St George's and Corporation street will both now close - the Deepdale retail park store was thought to have been one of those set for the axe earlier this week.
In total, some 37 jobs are set to disappear in Preston.
The budget retailer is also closing its warehouse and distribution network, alongside its head office in Normanton, West Yorkshire, leading to the loss of 300 jobs.
Administrators have announced the closure of 145 Poundworld stores already.
Poundworld fell into administration on June 11, putting more than 5,100 jobs at risk across its 335-store portfolio.
Deloitte has been announcing tranches of store closures over the past two weeks after failing to find a buyer for the whole business.
Clare Boardman, joint administrator at Deloitte, said: "We would like to thank all the employees for their continued support and commitment during this difficult time. We are keeping staff appraised of developments as they happen."
The administrators are still in talks with some interested parties about selling parts of the remaining business, but hopes of saving a significant number of jobs has faded.
Deloitte has turned down a bid from company founder Chris Edwards, who was looking to save a raft of stores and safeguard around 3,000 jobs.
The founder of rival Poundland, Steven Smith, has also been linked to a bid to salvage part of Poundworld out of administration.
The collapse came amid decreasing footfall, rising costs and weak consumer confidence.
The budget retail chain, formerly owned by TPG Capital, is one of a number of retailers to call in administrators this year, with Toys R Us and Maplin disappearing from UK high streets.
The Gaucho restaurant group also fell into administration on Thursday, with the Cau chain being closed immediately, leading to the loss of 540 jobs.