As of the census of 2000, there were 4,224 people, 1,692 households, and 986 families residing in the village. The population density was 2,423.6/sq mi (937.3/km²). There were 1,745 housing units at an average density of 1,001.2/sq mi (387.2/km²). The racial makeup of the village was 79.24% White, 1.35% African American, 0.88% Native American, 4.40% Asian, 0.02% Pacific Islander, 11.55% from other races, and 2.56% from two or more races. Hispanic or Latino of any race were 35.35% of the population.
Rosemont was tied for first place in 2000 with Bowdon, Georgia, as the place in the United States with the highest percentage of people reporting Bulgarian ancestry. The percentage of people so reporting in 2000 was 2.7%.
There were 1,692 households out of which 29.4% had children under the age of 18 living with them, 43.3% were married couples living together, 8.9% had a female householder with no husband present, and 41.7% were non-families. 35.0% of all households were made up of individuals and 13.4% had someone living alone who was 65 years of age or older. The average household size was 2.50 and the average family size was 3.31.
In the village the population was spread out with 24.4% under the age of 18, 10.4% from 18 to 24, 35.7% from 25 to 44, 18.4% from 45 to 64, and 11.1% who were 65 years of age or older. The median age was 32 years. For every 100 females there were 110.7 males. For every 100 females age 18 and over, there were 111.2 males.
The median income for a household in the village was $34,663, and the median income for a family was $44,939. Males had a median income of $30,066 versus $30,015 for females. The per capita income for the village was $19,781. About 10.6% of families and 14.9% of the population were below the poverty line, including 23.6% of those under age 18 and 10.6% of those age 65 or over.
Rosemont has a station on Metra's North Central Service, which provides weekday rail service between Antioch, Illinois and Chicago, Illinois (at Union Station).
Rosemont also has a station on the CTA Blue Line of the Chicago 'L', which provides direct rail service to both O'Hare and Downtown Chicago.