Here's the SSA link to name popularity by state:
Olivia is #3 in NY, #24 in Texas, #26 in California...So it is popular everywhere, but it's a slightly variable popularity. I know plenty of people who thought a name was unpopular/uncommon because they didn't know any kids with it, only to be blindsided by its popularity for their own child. Kind of like when you leave an event early to avoid getting stuck in traffic and find out how many people had that exact same idea.
That's why the Baby Name Voyager that was mentioned in a previous post is such a good site for those of us concerned with name popularity; if a name is on an obvious upward trend, it can set off alarm bells.
One thing you might want to do if you want a name that is not too popular but still obviously a "real" name (of course that term is relative) is to check out the SSA's website and see what the incredibly popular names were 40, 50, or 60 years ago. My second daughter's name was the #2 name of the 1950s, but was #422 last year and is on a steady downward trend. So I can be assured that there won't be several other Lindas in her classes, but at the same time it's an easily recognizable name. (Sort of like my own; I've never met a Sabra, but every single person I've ever met knows another one. :LOL)