My dad used to work for Microsoft. 
Did he work at headquarters? It is located in Redmond, Washington.
Yes he did.
by revenue, and one of the world's most valuable companies. The word "Microsoft" is a portmanteau of "microcomputer" and "software". Microsoft is ranked No. 30 in the 2018 Fortune 500 rankings of the largest United States corporations by total revenue.
Microsoft was founded by Bill Gates and Paul Allen on April 4, 1975, to develop and sell BASIC interpreters for the Altair 8800. It rose to dominate the personal computer operating system market with MS-DOS in the mid-1980s, followed by Microsoft
to the State Route 520 and its floating bridge connecting Redmond to Seattle; the company did not want to delay the construction any further. Microsoft was ranked number 1 in the list of the World's Best Multinational Workplaces by the Great Place to Work Institute in 2011.
Corporate identity Headquarters.
The corporate headquarters, informally known as the Microsoft Redmond campus, is located at One Microsoft Way in Redmond, Washington. Microsoft initially moved onto the grounds of the campus on February 26, 1986, weeks before the company went public