As of the census of 2000, there were 95,745 people, 32,703 households, and 25,181 families residing in the county. The population density was 414 people per square mile (160/km²). There were 35,030 housing units at an average density of 152 per square mile (58/km²). The racial makeup of the county was 93.87% White, 1.63% Black or African American, 0.14% Native American, 1.24% Asian, 0.03% Pacific Islander, 1.67% from other races, and 1.42% from two or more races. 6.24% of the population were Hispanic or Latino of any race. 31.0% were of Italian, 21.1% Irish and 9.7% German ancestry according to Census 2000. 87.5% spoke English, 5.2% Spanish and 3.2% Italian as their first language. As of 2005 the population was estimated to be 86% non-Hispanic whites. African-Americans were now 2.6% of the population. 0.2% of the population was Native Americans. 1.9% was Asian. 9.2% of the population was Latino, representing a significant change in the ethnic make up of the county's population.
In 2000 there were 32,703 households out of which 38.90% had children under the age of 18 living with them, 65.40% were married couples living together, 8.30% had a female householder with no husband present, and 23.00% were non-families. 18.10% of all households were made up of individuals and 5.90% had someone living alone who was 65 years of age or older. The average household size was 2.86 and the average family size was 3.27. In the county the population was spread out with 26.50% under the age of 18, 6.30% from 18 to 24, 32.10% from 25 to 44, 25.60% from 45 to 64, and 9.60% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 99.50 males. For every 100 females age 18 and over, there were 97.30 males.
The median income for a household in the county was $72,279, and the median income for a family was $82,197(these figures had risen to $84,306 and $95,145 respectively as of a 2007 estimate). Males had a median income of $53,295 versus $38,390 for females. The per capita income for the county was $30,127. About 2.70% of families and 4.40% of the population were below the poverty line, including 4.50% of those under age 18 and 7.00% of those age 65 or over.
Putnam has two interstate highways. The east-west Interstate 84 comes in from the north near Ludingtonville, and connects to the southbound Interstate 684 in Southeast toward the Connecticut border. The Taconic State Parkway, another high-speed through road, runs north-south through central Putnam. US 9 runs north-south in the western part of the county, paralleled by NY 9D along the Hudson River. NY 22 runs north-south in the eastern part of the county. NY 301 runs east-west from Cold Spring to Carmel. The short NY 403 connects 9 and 9D near Garrison. Three of the region's major east-west routes traverse the eastern half of the county. NY 52 enters alongside I-84 from Dutchess County, to end at US 6 south of Carmel. East of Brewster, US 6 joins US 202 and the routes leave the county and state concurrently aside the interstate.
The county's highway and facilities department maintains a number of county roads and performs snow and ice control on portions of the following numbered highways within the county: U.S. Route 6 from Westchester County line to the NY 22/U.S. Route 202 concurrency; NY 6N for the entire duration within Putnam; NY 9D from NY 301 to the Dutchess County line; NY 52 from its southern terminus to NY 311; NY 164 for its entire duration, and NY 301 for its entire duration.
The county also has several passenger trains that travel through the county. The Harlem Line and the Hudson Line of the Metro-North Railroad run north-south in Putnam. The Harlem Line makes stops at Brewster, Southeast, and Patterson. The Hudson Line makes stops at Manitou, Garrison, Cold Spring, and Breakneck Ridge. A connection to Amtrak can be made to the south at Croton-Harmon in upper Westchester County or to the north at Poughkeepsie in Duchess County, both on the Hudson Line.