Google and Wikipedia are two very popular sites that a lot of people go to, to find the information or products that they are looking for. Despite being used for mostly the same reasons, there are fundamental differences between the two.
Google is generally a search engine that indexes web sites around the world. Searches on Google would result in links to the most related sites. On the other hand, Wikipedia resembles more of an online encyclopedia. It contains collated information from contributors all around the world.
Accuracy of the entered information is verified using a strict guideline and an army of dedicated volunteer editors, who look for incorrect information or intentional vandalisms and deal with them right away.
Wikipedia stores all the information and images that are entered into its own database and you would not be able to it using any other site when the Wikipedia site is down. In comparison, most of the search results that appear when you
search Google are from other websites; although some Google sites do appear when related to the query.
If for any reason the Google site goes down, you may still be able to search for the Sites using another search engine like those provided by Bing, Yahoo, and the multitude of not so popular search engines.
Since none of the links that Google presents is actually contained in their server, they have absolutely no control over the content of those websites. Although Google does have the
ability to remove any site from their database, this would mean removing the entire site from Google searches and not the questionable content alone. With Wikipedia, any inappropriate content is easily scanned and removed since they have full control over the content.
It is easier to compare these two to real world items that most people have already encountered. Google is more like a phonebook where you can look up the listed phone numbers.
Wikipedia is more like an encyclopedia where you look up the particulars of a certain topic. Both provide information but not in the same way.

Summary:
1. Google is a search engine while
Wikipedia is an online encyclopedia
2. Most of the content found in Google is
not hosted in Google servers while all of
the content found in Wikipedia is hosted
in Wikipedia servers
3. Google has no control over their
content while Wikipedia can quickly
sensor its content


Source: http://www.differencebetween.net/technology/internet/difference-betweem-google-and-wikipedia/

Everyone knws dis.
But I think it's wrong to believe Google doesn't have control over the contents coming from 3rd party sites (which are like 99.9 of wat appear on Google search).
Google can censor and filter websites easiliy and most unsuspectingly.
But though Wikipedia may have control over the contents on its websites, contributors add and modify its information easily and nearly unrestrictedly. As a result, people don't always feel comfortable using on Wikipedia.