A total of $2 million from the sale proceeds will be allocated for construction of the City Hub, while the remainder will be used to develop a new branch library.

The decision to sell was made in confidential session on Tuesday night.

Shellharbour Mayor Marianne Saliba said the council was "absolutely" happy with the sale and said the price had come in within expectations.

"This will help revitalise the Warilla town centre; new investment in Warilla is a good thing," Cr Saliba said.

The new owner is a company called Louis Mifsud & Nominees (Cel Bare Pty Ltd).

The sale includes an 18-month leaseback of the library, with a possible six-month extension, while the council investigates alternative sites for a library in the Warilla area.

A council spokeswoman said Shellharbour council was working with RSL representatives on a new location for the freedom wall and peace grove on the site.

However, Cr Peter Moran said the deal was not as good as first appeared.

Cr Moran said when councillors were first elected, they were told the sale of the chambers alone would raise $4 million.

The move to include the land containing the library and freedom wall in the expressions of interest campaign only occurred in December 2013.

"They have no idea how much it will cost to build a new Warilla Library, or even where it will go," Cr Moran said.

Cr Kellie Marsh said the sale was "extremely disheartening and disappointing".

"Nothing is safe in this city to fund this Taj Mahal," Cr Marsh said.

"We have lost a fantastic asset ... we basically gave it away."

Cr Saliba said a new Warilla Library would be close to the current site.

To have a new purpose-built library for Warilla come out of the process was a bonus as it was not something originally planned, she said.