I think you have an answer. Search for a utility locating service.
But this is such a great PSA, because so many don’t understand how 811 works. They think that 811 will locate everything for free. They will not. They usually reach out to the utility companies themselves, who only mark what they own (they do often use contractors, and it’s often the same one do multiple utilities). They will not mark the private lines that go on your property. Water and sewer lines are usually customer owned after the curb. Oftentimes gas and buried electric and communications as well.
By all means, call. Where theirs end is a great clue as to where your lines begin, and you might never know what might be running through some decades old easement. But just because you are clear doesn’t mean there is nothing there. And if it is damaged, it’s on you to fix if you own it.