| Year | Northeast | Northcentral | South | West |
| 1870 | 3.30% | 5.10% | 91.50% | 0.10% |
| 1880 | 3.50% | 5.90% | 90.50% | 0.20% |
| 1890 | 3.60% | 5.80% | 90.00% | 0.10% |
| 1900 | 4.40% | 5.60% | 89.70% | 0.30% |
| 1910 | 4.90% | 5.50% | 89.00% | 0.50% |
| 1920 | 6.50% | 7.60% | 85.20% | 0.80% |
| 1930 | 9.60% | 10.60% | 78.70% | 1.00% |
| 1940 | 10.60% | 11.00% | 77.00% | 1.30% |
| 1950 | 13.40% | 14.80% | 68.00% | 3.80% |
| 1960 | 16.10% | 18.30% | 60.00% | 5.70% |
| 1990 | 18.40% | 19.30% | 52.80% | 9.50% |