As a full time Realtor my opinion on Zillow is somewhat dismal...old,incomplete information. Zillow has a margin of error upto 9%!
Beware of using it as a reliable tool of any kind. Here's an example of Zillow. My home. Wrong built date (I suspect they're using plat dates rather than build dates. Nothing around here pre-dates statehood). Wrong sq. footage(they seem to miss add-ons). Wrong #of baths. Wrong high school (this is critical, people shop schools). Checked on other homes in the area and most were also similarly wrong or suspect. The pic is 3 years old. Its not like this is hard to find info, this neighborhood is over 90 years old. Going to the courthouse would give you much better info.
Strangely, they were within 10% of my estimate of value. Its fun to look at but just not accurate and gives an unsophisticated agent or buyer too many reasons to low ball.