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You may also go to the account settings on your gmail ( top right, click your picture) and select security,Recent activity->Review security-related events in your account.-> View All Events. That will give you extensive details on recent activity. Couple of times I noticed that my account was used from another state that is 7 hours away from where I am now. I looked at the ip address and when to an IP Locator website ,http://www.iplocation.net/index.php.to get more details on it . The IP's geographical location was pointing to my current location. Dont know how Google is showing this in a different location. May be they need a better GPS system, I don't know.
When you log-in to your gmail, scroll down to the bottom of your email list. On the bottom right, in tiny letters, it says, "last account activity." This will show when anyone last logged in. If you click the word "details" just under that, it will show the date and time of the last 10 activity events, how your account was accessed, and the IP address. I don't know of a way to see further back in time than that, perhaps someone else does. You can also set it up to alert you to any unusual activity while you are poking around there, so that Google will let you know if your account suddenly starts getting logged into with an IP address from Bulgaria or Russia or wherever.