DSDR KB:

You can do this with the PUMA equivalency files produced by the Census Bureau. The PUMA equivalency files document the counties that correspond to PUMAs and vice versa. For instance, there are small counties that are cumulated into a single PUMA and counties like Wayne county, Michigan that have multiple PUMAs. You can use this info to determine which PUMAs define a MSA, CMSA, etc.

Here is a link to the PUMA equivalency files as a directory:

http://www.psc.isr.umich.edu/dis/data/ref/PUMA/SUPERPUMA-2000-5pct.html(to look at)

If you are using this information in a statistical package, there is a database version of it the PUMA equivalency files:

http://www.psc.isr.umich.edu/dis/data/ref/PUMA/data.html

Click on the choices under Data.