According to the United States Census Bureau, the city has a total area of 18.0 square miles (46.7 km²) in Central Marshall County. 18.0 square miles (46.7 km²) of it is land and 0.04 square miles (0.1 km²) of it (0.11%) is water. Neighboring counties include Hardin and Grundy to the North, Tama County to the east, Jasper to the south, and Story County to the west.
Marshalltown Community College is located at the southern edge of town near the junction of US Highway 30 and Iowa Highway 14.
Marshalltown has a local bus service (Marshalltown Municipal Transit or MMT), taxicab services, shuttle car service to Des Moines International Airport, and is also served by Trailways Coach Nationwide.
A municipal airport serves the county approximately four miles north of town. The closest commercial flights are in Des Moines, 50 miles to the southwest.
There were 10,175 households out of which 30.0% had children under the age of 18 living with them, 50.5% were married couples living together, 10.8% had a female householder with no husband present, and 35.2% were non-families. 29.7% of all households were made up of individuals and 13.5% had someone living alone who was 65 years of age or older. The average household size was 2.44 and the average family size was 3.02.
In the city the population was spread out with 24.5% under the age of 18, 8.9% from 18 to 24, 26.0% from 25 to 44, 23.0% from 45 to 64, and 17.6% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 98.0 males. For every 100 females age 18 and over, there were 95.3 males.
The median income for a household in the city was $35,688, and the median income for a family was $45,315. Males had a median income of $32,800 versus $23,835 for females. The per capita income for the city was $19,113. About 8.8% of families and 12.5% of the population were below the poverty line, including 17.5% of those under age 18 and 10.6% of those age 65 or over.
Marshalltown has a relatively high Hispanic population compared to other towns in Iowa. This is largely due to the Swift meatpacking plant in Marshalltown, which employs many Latinos.
Marshalltown has two official sister cities. These are Minami-Alps in the Yamanashi prefecture of Japan and Budyonnovsk in Stavropol Krai, Russia.
The unofficial sister city of Marshalltown is Villachuato, Mexico. There is a symbiotic relationship between Marshalltown and Villachuato. Villachuato supplies about half of the workers to the Swift meatpacking plant. In 2001, then Mayor Floyd Harthun of Marshalltown saw firsthand the degree of interdependence between the two communities when he visited their sister city Villachauto. In the mayor's words, "I was being self serving. We need people." In addition to noting that about a third of the license plates in Villachuato were from Marshall County, Iowa, he also learned of the essential role of money sent by Villachuatans living in Marshalltown in providing electricity, underground water, road paving projects, and in restoring the town church and town plaza.
In 1996, the Swift meatpacking plant was raided by the INS and 148 Latino undocumented workers were arrested and deported.
Again on December 12, 2006 the Immigration and Customs Enforcement (I.C.E) staged a coordinated predawn raid at the Swift and Co meat packing plant in Marshalltown and at 5 other Swift plants in western states, interviewing workers and removing hundreds in buses. As a result, students in Marshalltown schools have expressed fears that federal agents will come to the schools, with teachers working to calm those fears. Many students, having lost a loved one, were concerned that they will also be taken away. According to the Des Moines Register, many Marshalltown families have been split up, and many children left without parents. In one case, the mother of a breastfeeding child was detained, leading to the refusal of the baby to eat, and initial attempts by church officials to find the status of the nursing mother were unsuccessful. According to the Des Moines Register, the timing of the raid is a key issue. The raid took place on the Feast of Our Lady of Guadalupe, who is a national symbol and religious icon for Mexicans. On this day, many Latinos pay tribute to her as a symbol of hope and protection.
The raid stemmed from a months long investigation into identity theft by illegal immigrants centered around the plant. Of the 90 workers arrested by ICE in Marshalltown, 2 were charged with identy theft.
Marshalltown has 6 elementary schools — Anson, Fisher, Franklin, Hoglan, Rogers, and Woodbury — 2 middle schools, and 1 high school. Aside from the elementary schools, these schools are Lenihan Intermediate School, Miller Middle School, and Marshalltown High School.
Fisher Elementary enrolls 346 students anywhere from K-4th grade. They currently employ 51 staff members.
Franklin Elementary was built in 1913. They currently enroll 400 students. They currently employ 60 staff members.
Lenihan Intermediate was built in 1965. Construction cost $775,000. It was designed to house 300 students. It was first a Catholic high school in 1904. After five years in operation the administrators of Lenihan High School found it was financially impossible to continue providing quality education for their young people. At the same time the public school in Marshalltown was overcrowded with students at the junior high level. The solution decided upon by both parties was to sell Lenihan to the public school and to make the school a 7, 8, 9 junior high. The transaction was completed and Lenihan Junior High became a reality in the fall of 1970. The Catholic school name, mascot and school colors were all retained in the new public junior high school.
The need for additional space at Lenihan Junior High resulted in the construction of six rooms on the east side of the building in 1975. The addition consisted of three regular classrooms, an art room and two industrial arts facilities.
In the late 1970’s Lenihan Junior High’s enrollment was in the 470’s but then declined to a total of approximately 400 students. In 1984 the 6th grade was added to the school which briefly put the enrollment over 500. However, with declining enrollment the school housed between 400-450 students in grades 6-9 in the later part of the 1980’s. In the spring of 1988, the school board voted to close Lenihan at the end of the 1989 school year.