Mildred is located at 38°1'22N, 95°10'25W (38.022777, -95.173512). According to the United States Census Bureau, the city has a total area of 0.6 km² (0.2 mi²), all land.
As of the census of 2000, there were 36 people, 19 households, and 9 families residing in the city. The population density was 57.9/km² (151.7/mi²). There were 24 housing units at an average density of 38.6/km² (101.1/mi²). The racial makeup of the city was 94.44% White, and 5.56% from two or more races.
There were 19 households out of which 21.1% had children under the age of 18 living with them, 26.3% were married couples living together, 10.5% had a female householder with no husband present, and 52.6% were non-families. 52.6% of all households were made up of individuals and 15.8% had someone living alone who was 65 years of age or older. The average household size was 1.89 and the average family size was 2.89.
In the city the population was spread out with 22.2% under the age of 18, 8.3% from 18 to 24, 27.8% from 25 to 44, 25.0% from 45 to 64, and 16.7% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 111.8 males. For every 100 females age 18 and over, there were 115.4 males.
The median income for a household in the city was $21,250, and the median income for a family was $14,167. Males had a median income of $20,625 versus $11,250 for females. The per capita income for the city was $8,372. There were 16.7% of families and 15.6% of the population living below the poverty line, including 18.2% of under eighteens and none of those over 64.