If you regularly log into Google, and especially if your phone is an Android or connects to Google Maps, the default is for Google to track your location history. While logged into Google, click here:
and choose a date. I just discovered that my entire movement history since I bought my current phone in December of 2013 are tracked by default. I suppose this is a safety feature if I go missing, but it’s a little creepy. You can turn off the default tracking.