As far as I can tell (in December 2013) ...
Douglas Crockford's master source repository for "json.org" is now on GitHub - https://github.com/douglascrockford/JSON-java. (The GIT history starts in 2010, and the latest change in "master" is a couple of weeks ago.)
Paul Merlin (aka "eskatos") has Mavenized the code: https://github.com/eskatos/org.json-java
Binary "org.json" JAR files are "regularly" built from Paul Merlin's tree and pushed to Maven Central. You can find them via the "here" link in Paul's README.md file; see the line above.
There are other older (pre-2010) binary releases of the "org.json" JAR file in Maven Central under various guises; review the search results for this link" http://mvnrepository.com/search.html?query=org.json.
The copyright dates in the "org.json" source code don't mean much. They clearly aren't updated when the code is updated. However, Douglas Crockford does update the @version javadoc tags, at least in some commits.
UPDATE (December 2016)
As of some time in 2015, Douglas Crockford has passed ownership of the Github repository to Sean Leary. The old Github URL for the project now redirects to https://github.com/stleary/JSON-java. The project continues to be relatively active.
See also: Where has json.org java library gone?
I would recommend using json-simple or one of the other JSON libraries for Java that have developed. This has features the JSON.org API lacks (and I think it will stay that way).
For instance, the json-simple version of JSONObject implements Map and JSONArray implements List. It also has other features, like a SAX-style API.
Probably your simple json.jar file isn't in your classpath.
I was facing same issue in my Spring Integration project. I added below JSON dependencies in pom.xml file. It works for me.
<dependency>
<groupId>org.json</groupId>
<artifactId>json</artifactId>
<version>20090211</version>
</dependency>
A list of versions can be found here: https://mvnrepository.com/artifact/org.json/json