According to the United States Census Bureau, the city has a total area of 1.5 square miles (3.8 km²), all of it land.
There were 704 households out of which 36.9% had children under the age of 18 living with them, 53.1% were married couples living together, 12.5% had a female householder with no husband present, and 30.0% were non-families. 26.4% 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 2.61 and the average family size was 3.18.
In the city the population was spread out with 28.1% under the age of 18, 9.0% from 18 to 24, 27.3% from 25 to 44, 21.1% from 45 to 64, and 14.6% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 90.3 males. For every 100 females age 18 and over, there were 88.4 males.
The median income for a household in the city was $27,188, and the median income for a family was $34,188. Males had a median income of $30,337 versus $16,607 for females. The per capita income for the city was $12,814. About 21.6% of families and 23.3% of the population were below the poverty line, including 28.0% of those under age 18 and 24.8% of those age 65 or over.
South Texas locals often use Three Rivers as a "halfway point" between San Antonio and Corpus Christi, TX because it is located approximately from both and is just off I-37, which is the most commonly used freeway to travel between the two cities.
There is a single school district for the entire city, Three Rivers Independent School District, containing Three Rivers Elementary School, Three Rivers Junior High School and Three Rivers High School. The school mascot is the bulldog, and the school has a usually-friendly rivalry with the school district in neighboring George West, TX. For the 2007 year, the school will compete in UIL events in District 31 - AA. In 1996 Wade Bonnell caught the wining touchdown pass in over time to save homecoming he is the town HERO.
Recently, Three Rivers began celebrating an annual one-day festival celebrating the popular chip dip in the area, calling it Salsa Fest. Each year in the spring, competitors may enter an original salsa recipe to be judged by festival-goers willing to pay the $1 voting fee. Currently, there are three divisions one can enter their salsa in: Amateur (anyone may enter); Professional (if the entering salsa is currently sold commercially); and Restaurant (restaurants can enter the homemade salsa served with their meals) to allow fairness between a homemade salsa and one that is commercialized. Voters vote for their favorite salsa in each division, allowing for three grand-prize winners who are rewarded with money and a Commemorative plaque, for their efforts.
Three Rivers currently has an unusually thriving music scene for a town of its size, with at least 10 rock bands and numerous pop and country artists residing in the community, many of which have performed at Three Rivers Salsa Festival.
Three city parks in total are available for visit, free of charge, although at Three Rivers City Park, located on Oakville Road, between the school and cemetery, $1 is required to use the swimming pool. This park also includes a soccer field used by Little League Soccer teams in the area, and two baseball diamonds, both used by Little League teams as well. The other two parks are the aforementioned park in The Barrio, and Tips Park also at the west end of town, off Hwy 72, which has camping and RV accommodations (for a fee), and fishing access to the Frio River.
Many Three Rivers residents live in or near Three Rivers because of the large number of jobs needed in the nearby federal prison (located roughly west of town, on Hwy 72) and the Valero refinery located inside the city limits. Most new residents moving permanently to Three Rivers are ones transferred to the prison or refinery from other jobs within those respective systems.
Most visitors to Three Rivers who come for reasons other than business or visiting family often come to stay overnight in one of several hotels because of Three Rivers' proximity to Choke Canyon Lake where several bass fishing tournaments are held each year. Other reasons for visit include hunting (whitetail deer, wild hog, dove, and quail are hunted in the area to name a few), shopping, the Live Oak County Jamboree, the Live Oak County Fair, and using the town as a temporary resting place in a trip, as the nearby highways (I-37, Hwy 281, and Hwy 72) joining nearby or in Three Rivers make a junction for travelers coming to and from San Antonio, Corpus Christi, and the Rio Grande Valley.
There are three stoplights as of 2006 on US Highway 281, two at the two intersections of Texas Highway 72, and one where Hwy 281 intersects Alexander St.
Three Rivers is also the site of the first glass factory in the State of Texas. Although it is no longer in production and the building has been demolished, a State Historical Marker stands at its site. Some of the antique shops in town and in the neighboring town of George West may sometimes carry a few pieces the factory produced.
American Pop trio The Jonas Brothers own a ranch in Three Rivers
In 1949, the community received attention concerning a dispute about the burial of Felix Longoria.