According to the National Community College Benchmark Project 2008 report: 

17% of community college graduates completed a degree or certificate within three years and 18% transferred within three years.

The fall to spring semester persistence rate (students who continued to enroll) was 69% and the fall to next fall semester persistence rate (students who continued to enroll) was 47%. Community colleges may be judged on their degree completion rates but many students’ education goals at community colleges do not necessarily involve attaining a degree or certificate. Colleges do worry about that fall to fall persistence rate. That means every fall one half of the students on campus are new (or at least have been away for a while.)

USA Today had an article this morning about 4-year college graduate 53% of students in 6 years.  At a university, 4-year college, a person is there to get a degree. While at a community college, there are many learning objectives: including personal enrichment, specific training courses, preparation for transfer to a college/university, and degree and certificate obtainment. Many students at CC already have 4-year degrees. 
Michael Lesiecki