The company took journalists on a tour of where it all started - Susan Wojcicki's garage in Menlo Park, California, where Larry Page and Sergey Brin began working on Google in 1998. Wojcicki is currently a Google vice president.
A Google+ page meanwhile included a photo album of the original home search page, and collected dozens of birthday wishes.
But Google, which has grown into one of the world's biggest companies, was not content to just look at the past. It announced an upgrade to its main search engine, with new ways to integrate its use across different devices.
Since 1998, the tech world has changed dramatically and Google said its search engine has been constantly improved.
"The world has changed so much since then, billions of people have come online, the web has grown exponentially, and now you can ask any question on the powerful little device in your pocket," said Google Search chief Amit Singhal in a blog post.
"You can explore the world with the Knowledge Graph, ask questions aloud with voice search, and get info before you even need to ask with Google Now."
Singhal said the change includes 'a simpler, more unified design on mobile devices.'
"You'll also notice a new look and feel for Google Search and ads on your phones and tablets," he added.
"It's cleaner and simpler, optimised for touch, with results clustered on cards so you can focus on the answers you're looking for."
Danny Sullivan of the tech blog Search Engine Land said the upgrade of main search engine is based on a new algorithm with the code name "Hummingbird," which he said is "especially designed to handle complex queries."