According to the State of California Department of Justice [0], the last publicly acknowledged data breach from Google was March 9th, 2017. Before that it was August 10th, 2016, and before that March 29th, 2016.
Here's a quote from one of them:
"We recently learned that certain hotel reservations made for Google business travel were among the many reservations affected by a security incident impacting a third-party provider’s electronic reservation system that serves thousands of travel agencies and hotels. This did not affect Google’s systems. However, this incident impacted one of the travel providers used by Googlers, Carlson Wagonlit Travel (CWT)."