The building at 367 Addison Avenue, Palo Alto has been credited as "the birthplace of Silicon Valley".
"The HP garage has become a symbol of what can rise from humble beginnings with hard work and determination," said Gary Elliott, vice president of HP's brand management and design division.
"It is an honour to be recognised and we hope that it will further spread these core HP values to a national audience."
The garage was part of a house originally built for Dr John Spencer, the first mayor of Palo Alto.
Packard discovered the garage behind the house, which he was renting, in 1938. The following year he and Hewlett started a company out of the garage with $538 in working capital that consisted of cash and a second-hand drill press.
HP moved out of the garage in 1940, but the company would later push to have the site declared an historic landmark in the 1980s. HP bought the property in 2000.
The company finished restoring the house and the garage in 2005. Both buildings are closed to the public, although the company allows visitors to photograph the garage and house from the outside.
The new designation is largely symbolic, as the building has been protected under state law since 1987 when California declared it an historic landmark.
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