As of the census of 2000, there were 101,355 people, 42,615 households, and 17,599 families residing in the city. The population density was 15,766.1 people per square mile (6,086.1/km²), making Cambridge the fifth most densely populated city in the U.S. and the second most densely populated city in Massachusetts behind neighboring Somerville. There were 44,725 housing units at an average density of 6,957.1/sq mi (2,685.6/km²). The racial makeup of the city was 68.10% White, 11.92% Black or African American, 0.29% Native American, 11.88% Asian, 0.08% Pacific Islander, 3.19% from other races, and 4.56% from two or more races. 7.36% of the population were Hispanic or Latino of any race. This rather closely parallels the average racial demographics of the United States as a whole, although Cambridge has significantly more Asians than the average, and fewer Hispanics and Caucasians. 11.0% were of Irish, 7.2% English, 6.9% Italian, 5.5% West Indian and 5.3% German ancestry according to Census 2000. 69.4% spoke English, 6.9% Spanish, 3.2% Chinese or Mandarin, 3.0% Portuguese, 2.9% French Creole, 2.3% French, 1.5% Korean and 1.0% Italian as their first language.
There were 42,615 households out of which 17.6% had children under the age of 18 living with them, 29.1% were married couples living together, 9.7% had a female householder with no husband present, and 58.7% were non-families. 41.4% of all households were made up of individuals and 9.2% had someone living alone who was 65 years of age or older. The average household size was 2.03 and the average family size was 2.83.
In the city the population was spread out with 13.3% under the age of 18, 21.2% from 18 to 24, 38.6% from 25 to 44, 17.8% from 45 to 64, and 9.2% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 96.1 males. For every 100 females age 18 and over, there were 94.7 males.
The median income for a household in the city was $47,979, and the median income for a family was $59,423 (these figures had risen to $58,457 and $79,533 respectively as of a 2007 estimate). Males had a median income of $43,825 versus $38,489 for females. The per capita income for the city was $31,156. About 8.7% of families and 12.9% of the population were below the poverty line, including 15.1% of those under age 18 and 12.9% of those age 65 or over.
Cambridge was ranked as one of the most liberal cities in America. Its residents jokingly refer to it as "The People's Republic of Cambridge." Its FY 2007 residential property tax rate, $7.48 per $1000 of assessed valuation, is one of the lowest in Massachusetts. Cambridge enjoys the highest possible bond credit rating, AAA, with all three Wall Street rating agencies.
Cambridge is noted for its diverse population, both racially and economically. Residents, known as Cantabrigians, range from affluent MIT and Harvard professors to working-class families to immigrants. The first legal applications in America for same-sex marriage licenses were issued at Cambridge's City Hall.
Cambridge is also the birthplace of Thai king Bhumibol Adulyadej (Rama IX), who is the world's longest reigning monarch at age 80 as well as the longest reigning monarch in Thai history. He is also the first king of a foreign country to be born in the United States.
Several major roads lead to Cambridge, including Route 2, Route 16 and the McGrath Highway (Route 28). The Massachusetts Turnpike does not pass through Cambridge, but provides access by an exit in nearby Allston. Both U.S. Route 1 and I-93 (MA) also provide additional access on the eastern end of Cambridge at Leverett Circle in Boston. Route 2A runs the length of the city, chiefly along Massachusetts Avenue. The Charles River forms the southern border of Cambridge and is crossed by eleven bridges connecting Cambridge to Boston, eight of which are open to motorized road traffic.
Cambridge has an irregular street network because many of the roads date from the colonial era. Contrary to popular belief, the road system did not evolve from longstanding cow-paths. Roads connected various village settlements with each other and nearby towns, and were shaped by geographic features, most notably streams, hills, and swampy areas. Today, the major "squares" are typically connected by long, mostly straight roads, such as Massachusetts Avenue between Harvard Square and Central Square, or Hampshire Street between Kendall Square and Inman Square.
Cambridge has the Porter stop on the regional Commuter Rail, the Lechmere stop on the Green Line, and five stops on the Red Line. Alewife Station, the current terminus of the Red Line, has a large multi-story parking garage (at a rate of $7 per day as of 2009). The Harvard Bus Tunnel, under the Square, reduces traffic congestion on the surface, and connects to the Red Line underground. This tunnel was originally opened for streetcars in 1912, and served trackless trolleys and buses as the routes were converted. The tunnel was partially reconfigured when the Red Line was extended to Alewife in the early 1980s.
Cambridge has several bike paths, including one along the Charles River, the Minuteman Bikeway and the Linear Park connecting Alewife and the Somerville Community Path. Bike parking is common and there are bike lanes on many streets, although concerns have been expressed regarding the suitability of many of the lanes. From time to time, police target their traffic enforcement efforts towards bicyclists who do not follow the Rules of the Road for vehicles, especially going through red lights, failure to stop for pedestrians at unsignalized crosswalks, riding on the wrong side of the street or the wrong way on a one-way street, and riding without a headlight at night. In addition, Cambridge bans cycling on certain sections of sidewalk where pedestrian traffic is heavy.
While Bicycling Magazine has rated Boston as one of the worst cities in the nation for bicycling (In their words, for "lousy roads, scarce and unconnected bike lanes and bike-friendly gestures from City Hall that go nowhere – such as hiring a bike coordinator in 2001, only to cut the position two years later"), it has listed Cambridge as an honorable mention as one of the best and was called by the magazine "Boston's Great Hope." Cambridge has an active, official bicycle committee.
Walking is unusually popular in Cambridge. Census data from 2000 show that, of American communities in excess of 100,000 residents, Cambridge has the highest percentage of commuters who walk to work. Cambridge's major historic squares have been recently adapted into a modern walking landscape, which has sparked a traffic calming program based on pedestrian rather than motorist needs.
Intercity transport is found in Boston, which is adjacent to Cambridge. Intercity buses and Amtrak stop at South Station in Boston, while Logan International Airport is located in East Boston across Boston Harbor from the downtown area. The MBTA also has numerous subway stations in Cambridge and nearby cities and towns that are shared with the regional commuter rail lines it operates.