* Student enrollment: This is the most common metric. The average student enrollment can range from a few hundred to tens of thousands, with a significant number falling in the range of several thousand students. There's no reliable single source for a precise average across all community colleges in the US (or globally).
* Number of faculty and staff: This will naturally correlate with student enrollment. Larger colleges will have proportionally larger staffs.
* Physical size (campus area): This varies wildly. Some are located on small urban campuses, while others have sprawling rural campuses.
To find the average for a specific region or state, you'd need to consult the relevant state's higher education authority or a national database of community colleges. Even then, the average will be just a statistical representation and will mask the significant variation in actual sizes.