The city straddles approximately three miles of Interstate 35 from less than a mile southwest of its junction with Interstate 635 south to 75th Street. Shawnee Mission Parkway, an east-west road, nearly bisects the city. U.S. Routes 59 and 69 follow the Interstate to the south of the city and follow Shawnee Mission Parkway to the east from its junction with the Interstate. Turkey Creek, following a roughly parallel path to the Interstate, flows through the city.
Every year, Merriam hosts the Turkey Creek Festival, an arts and crafts show with plenty of other family activities. On Wednesday nights during the summer, Merriam also hosts Music at the Marketplace, free outdoor concerts for the whole family.
Merriam is located at 39°1'15N, 94°41'38W (39.020888, -94.693784). According to the United States Census Bureau, the city has a total area of 11.2 km² (4.3 mi²), all land.
Merriam's population was estimated to be 10,769 in the year 2005, a decrease of 232, or -2.1%, over the previous five years.
As of the U.S. Census in 2000, there were 11,008 people, 4,839 households, and 2,903 families residing in the city. The population density was 983.8/km² (2,550.9/mi²). There were 5,042 housing units at an average density of 450.6/km² (1,168.4/mi²). The racial makeup of the city was 89.24% White, 4.02% Black or African American, 0.42% Native American or Alaska Native, 2.09% Asian, 0.02% Pacific Islander, 1.95% from other races, and 2.25% from two or more races. Hispanic or Latino of any race were 5.41% of the population. 21.9% were of German, 12.9% English, 11.5% Irish and 7.7% American ancestry according to Census 2000.
There were 4,839 households out of which 26.3% had children under the age of 18 living with them, 46.8% were married couples living together, 9.7% had a female householder with no husband present, and 40.0% were non-families. 33.3% of all households were made up of individuals and 7.6% had someone living alone who was 65 years of age or older. The average household size was 2.23 and the average family size was 2.86.
In the city the population was spread out with 21.7% under the age of 18, 8.3% from 18 to 24, 34.0% from 25 to 44, 23.8% from 45 to 64, and 12.2% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 92.6 males. For every 100 females age 18 and over, there were 90.9 males.
The median income for a household in the city was $48,455, and the median income for a family was $54,639. Males had a median income of $37,358 versus $29,815 for females. The per capita income for the city was $23,988. About 4.3% of families and 6.2% of the population were below the poverty line, including 9.7% of those under age 18 and 7.1% of those age 65 or over.