Campaigners have successfully raised $6.7 million (£3.6-4.2 million) and secured Mies van der Rohe's seminal Farnsworth House at a Sotheby's auction in New York last Friday.
A coalition of the National Trust for Historic Preservation, the Landmark Preservation Council and the Friends of Farnsworth House raised the cash in a last ditch bid to 'save the building from falling into the hands of owners that fail to respect it'.
The conservationists, who were up against just one other anonymous telephone bidder at the auction, only came out on top because of a last-minute $3 million contribution to their fighting fund.
The victory means concerns about the building's future - including speculation that it could be moved to a new location - can now be laid to rest.
The site will be opened to the public as a museum after essential repairs are carried out.
The campaign to save the building was reinvigorated after Governor Rod Blagojevich re-entered the battle after an original plan for the state government to buy the building collapsed. He called on public sector organisations to stump up the funds required to buy the property from British developer Peter Palumbo.
The one-storey house was described by Sotheby's senior vice-president James Zemaitis as the most successful application of Mies' theories.
Campaigners said they were delighted with the auction's outcome. 'The Farnsworth House is one of the most significant houses built in the US in the 20th century, ' Landmark Preservation Trust president David Bahlman said.
'We are thrilled it will be protected forever and made available to the public, particularly to architects and students of architecture, ' he added.
And the comments were echoed on this side of the Atlantic. Docomomo's Dennis Sharp said the news was 'terrific'. 'This is one of those buildings that one always hopes will not get into the wrong hands, ' he said. 'But thankfully it now seems that the right people will be able to look after it.'
'If only the conservation lobby would do the same kind of thing over here and recognise that it is worth spending some money to save Modernist masterpieces such as Greenside, ' he added.