It has had no county government since July 1, 1998, when all former county functions were assumed by other governmental agencies. There are vestiges of the old system: for example, county sheriffs are still elected, but are under the state Executive Office of Public Safety.

Also, the office of district attorney, currently held by John Conte, is effectively a county-wide position even though the district includes one town from a neighboring county. There is not, however, a county council or a commissioner. Communities are now granted the right to form their own regional compacts for sharing services.

When the government of Worcester County was established on April 2, 1731, Worcester was chosen as its shire town (later known as a county seat). From that date until the dissolution of the county government, it was the only county seat. Because of the size of the county, there were fifteen attempts over 140 years to split the county into two counties, but without success.

Initially, Lancaster was proposed as the seat of the northern county; later, Petersham was proposed once and Fitchburg was proposed repeatedly, most recently in 1903. Perhaps as a concession, in August 1884, the Worcester County Registry of Deeds was split into two, with the Worcester Northern registry placed in Fitchburg.

As of the census of 2000, there were 750,963 people, 283,927 households, and 192,502 families residing in the county. The population density was 192/km (496/mi). There were 298,159 housing units at an average density of 76/km (197/mi).

The racial makeup of the county was 89.61% White, 2.73% Black or African American, 0.25% Native American, 2.62% Asian, 0.04% Pacific Islander, 2.93% from other races, and 1.82% from two or more races. 6.77% of the population were Hispanic or Latino of any race.

There were 283,927 households out of which 33.60% had children under the age of 18 living with them, 52.50% were married couples living together, 11.40% had a female householder with no husband present, and 32.20% were non-families. 26.20% of all households were made up of individuals and 10.40% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.11.

In the county the population was spread out with 25.60% under the age of 18, 8.40% from 18 to 24, 31.10% from 25 to 44, 21.80% from 45 to 64, and 13.00% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 95.50 males. For every 100 females age 18 and over, there were 92.10 males.

The median income for a household in the county was $47,874, and the median income for a family was $58,394. Males had a median income of $42,261 versus $30,516 for females. The per capita income for the county was $22,983. About 6.80% of families and 9.20% of the population were below the poverty line, including 11.30% of those under age 18 and 9.50% of those age 65 or over.