1. Venus (7) (AR, FL, KY, MO, NE, OR, PA)
2. Earth + Earth-name variations (7) (TX, WI, MN x2, MO, MD x2) ***
3. Neptune (6) (IA, OH, TN, WV, WI) **CA
4. (tie) Jupiter (3) (CA, FL, NC)
4. (tie) Mercury (3) (AL, NV, TX)
4. (tie) Pluto (3)* (MS, TX, WV)
4. (tie) Mars (3) (CA, PA, TX)
8. Saturn (2) (IN, TX)
9. Uranus (1) (Technically a topographic feature in ID)
*Due to recent non-planetlike activity, Pluto is ineligible for post-season play
**Update: I have added Neptune, CA, which A.M. noticed I was missing
***There is the argument (made eloquently by A.M. in the comments) that Earth's six Earth-name variations, such as "Black Earth," should count as a Division I-AA victories and that Neptune should claim the second spot based on SOS (Strength of Schedule).
Source: U.S. Geological Survey Geographic Names Information System
Commentary: Barry Sanders' planet needs at least one more U.S. town named after it to qualify for the Bowl Championship game.