Major highways

• Interstate 80 – runs east-northeast across the southern portion of the county, passing Dexter and De Soto on its way to Des Moines
• U.S. Highway 6 – from its starting point in Adel, runs east across the midsection of the county on its way to Des Moines
• U.S. Highway 169 – runs north–south through the center of the county, from Bouton to Adel to De Soto
• Iowa Highway 17 – from its starting point (intersection with Iowa 141) at Granger, runs north along the county's eastern boundary, into Boone County
• Iowa Highway 44 – runs east–west through the center of the county, through Dallas Center
• Iowa Highway 141 – runs east across northern portion of county, through Dawson, Perry, Bouton and Woodward, then southeast to exit into Polk County at Granger
• Iowa Highway 144 - from its starting point (intersection w Iowa 141) at Perry, runs north into Boone County
• Iowa Highway 210 – from its starting point (intersection w Iowa 141), runs north to Woodward and continues into Boone County^[7]

Adjacent counties

• Adair County – southwest
• Boone County – north
• Greene County – north and northwest
• Guthrie County – west
• Madison County – south
• Polk County – east
• Warren County – southeast

2020 census

The 2020 census recorded a population of 99,678 in the county, with a population density of 168.7353/sq mi (65.1491/km²). 94.19% of the population reported being of one race. There were 41,125 housing units of which 38,291 were occupied.^[1]

2010 census

The 2010 census recorded a population of 66,135 in the county, with a population density of 112.7698/sq mi (43.5407/km²). There were 27,260 housing units, of which 25,240 were occupied.^[15]

2000 census

As of the census^[16] of 2000, there were 40,750 people, 15,584 households, and 11,173 families in the county. The population density was 70 inhabitants per square mile (27/km²). There were 16,529 housing units at an average density of 28 per square mile (11/km²). The racial makeup of the county was 94.75% White, 0.74% Black or African American, 0.15% Native American, 0.69% Asian, 0.04% Pacific Islander, 2.79% from other races, and 0.84% from two or more races. 5.40% of the population were Hispanic or Latino of any race.

Of the 15,584 households, 37.20% had children under the age of 18 living with them, 60.60% were married couples living together, 8.00% had a female householder with no husband present, and 28.30% were non-families. 23.60% of households were one person and 8.20% were one person aged 65 or older. The average household size was 2.59 and the average family size was 3.08.

The age distribution was 28.20% under the age of 18, 6.90% from 18 to 24, 32.10% from 25 to 44, 21.60% from 45 to 64, and 11.10% 65 or older. The median age was 35 years. For every 100 females, there were 97.70 males. For every 100 females age 18 and over, there were 93.80 males.

The median household income was $48,528 and the median family income was $58,293. Males had a median income of $37,243 versus $27,026 for females. The per capita income for the county was $22,970. About 4.00% of families and 5.60% of the population were below the poverty line, including 6.10% of those under age 18 and 7.10% of those age 65 or over.

Cities

‡ partly in Polk County

Unincorporated communities

• Booneville

Townships

Population ranking

The population ranking of the following table is based on the 2020 census of Dallas County.^[1]

† county seat