| Region | 2000 | 2005 | 2010 | 2015 | 2020 | 2025 | 2030 | ||
| U.S. | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | ||
| Northeast | 19.0 | 18.5 | 18.1 | 17.5 | 17.0 | 16.4 | 15.9 | ||
| Midwest | 22.9 | 22.3 | 21.8 | 21.3 | 20.7 | 20.0 | 19.4 | ||
| South | 35.6 | 36.2 | 36.8 | 37.4 | 38.0 | 38.7 | 39.4 | ||
| West | 22.5 | 22.9 | 23.4 | 23.8 | 24.3 | 24.8 | 25.3 |