| Lewis & Clark County Residents |
| 1980: | 43,039 |
| 1990: | 47,495 |
| 2000: | 55,716 |
| 2003 estimate: | 57,137 |
| Percent change, 1990–2000: | 17.3% |
| U.S. rank in 2000: | 847th (for counties; state rank 6th) |
| City Residents |
| 1980: | 23,938 |
| 1990: | 24,699 |
| 2000: | 25,780 |
| 2003 estimate: | 26,718 |
| Percent change, 1990–2000: | 2.8% |
| U.S. rank in 2000: | Not reported |
| Density: | 1,840.7 people per square mile (2000) |
| Racial and ethnic characteristics | (2000) |
| White | 24,434 |
| Black or African American | 59 |
| American Indian and Alaska Native | 541 |
| Asian | 201 |
| Native Hawaiian and Pacific Islander | 18 |
| Hispanic or Latino (may be of any race) | 430 |
| Other | 98 |
| Percent of residents born in state: | 55.5% (2000) |
| Age characteristics | (2000) |
| Population under 5 years old | 1,501 |
| Population 5 to 9 years old | 1,558 |
| Population 10 to 14 years old | 1,628 |
| Population 15 to 19 years old | 1,962 |
| Population 20 to 24 years old | 1,999 |
| Population 25 to 34 years old | 2,931 |
| Population 35 to 44 years old | 3,919 |
| Population 45 to 54 years old | 4,309 |
| Population 55 to 59 years old | 1,414 |
| Population 60 to 64 years old | 975 |
| Population 65 to 74 years old | 1,640 |
| Population 75 to 84 years old | 1,403 |
| Population 85 years and older | 541 |
| Median age | 38.8 years |
| Births | (2002) |
| Five year average | 12.1 per 1000 population (county) |
| Deaths | (2002) |
| Five year average | 7.9 per 1000 population (county) |
| Money income | (2000) |
| Per capita income | $20,020 |
| Median household income | $34,416 |
| Total households | 11,476 |
| Number of households with income of . . . | |
| less than $10,000 | 1,438 |
| $10,000 to $14,999 | 908 |
| $15,000 to $24,999 | 1,725 |
| $25,000 to $34,999 | 1,767 |
| $35,000 to $49,999 | 1,809 |
| $50,000 to $74,999 | 2,228 |
| $75,000 to $99,999 | 911 |
| $100,000 to $149,999 | 464 |
| $150,000 to $199,999 | 130 |
| $200,000 or more | 96 |
| Percent of families below poverty level: | 9.3% (58.3% of which were female householder families in poverty) |
| 2002 FBI Crime Index Total: | Not reported |