| Region 4 | ||||||||
| Number of Registered Voters | ||||||||
| Source: Office of the Secretary of State | ||||||||
| 1994 | 1996 | 1998 | 2000 | 2002 | 2004 | 2006 | 2008 | |
| Ada | 146,661 | 172,224 | 162,683 | 181,292 | 170,696 | 208,168 | 202,073 | 233,037 |
| Boise | 3,515 | 4,087 | 4,496 | 5,007 | 4,357 | 4,998 | 4,643 | 5,145 |
| Elmore | 8,929 | 10,820 | 9,567 | 11,236 | 9,196 | 11,127 | 10,054 | 11,881 |
| Valley | 5,477 | 5,811 | 5,920 | 6,158 | 5,298 | 6,254 | 6,248 | 7,049 |
| * Population 18 years | ||||||||
| * This data is for the general elections of the reported years. | ||||||||