Portal is located at . According to the United States Census Bureau, the city has a total area of, all land.
Economy
Because Portal is in the Bakken Oil Field region, the cost of living has risen considerably in recent years. A 2015 speech by a U.S. Customs and Border Protection official used Portal as an example of an area where the cost of living, combined with limited housing availability, and the distance from medical care and shopping, can make it difficult to attract employees for federal government positions. The Portal State Bank, built in 1903, is on the National Register of Historic Places. The William E. Metzger House, built in 1904 - 1905, is also on the National Register of Historic Places
As of the census of 2010, there were 126 people, 61 households, and 38 families residing in the city. The population density was. There were 80 housing units at an average density of. The racial makeup of the city was 96.0% White, 0.8% African American, 2.4% Native American, and 0.8% from two or more races. Hispanic or Latino of any race were 4.0% of the population. There were 61 households of which 23.0% had children under the age of 18 living with them, 49.2% were married couplesliving together, 9.8% had a female householder with no husband present, 3.3% had a male householder with no wife present, and 37.7% were non-families. 31.1% of all households were made up of individuals and 8.2% had someone living alone who was 65 years of age or older. The average household size was 2.07 and the average family size was 2.58. The median age in the city was 46.6 years. 19% of residents were under the age of 18; 8.7% were between the ages of 18 and 24; 18.3% were from 25 to 44; 40.4% were from 45 to 64; and 13.5% were 65 years of age or older. The gender makeup of the city was 54.8% male and 45.2% female.
2000 census
As of the census of 2000, there were 131 people, 63 households, and 43 families residing in the city. The population density was 232.8 people per square mile. There were 98 housing units at an average density of 174.1 per square mile. The racial makeup of the city was 99.24% White and 0.76% Native American. There were 63 households out of which 19.0% had children under the age of 18 living with them, 63.5% were married couples living together, 3.2% had a female householder with no husband present, and 31.7% were non-families. 31.7% of all households were made up of individuals and 14.3% had someone living alone who was 65 years of age or older. The average household size was 2.08 and the average family size was 2.58. In the city the population was spread out with 17.6% under the age of 18, 1.5% from 18 to 24, 24.4% from 25 to 44, 38.9% from 45 to 64, and 17.6% who were 65 years of age or older. The median age was 48 years. For every 100 females, there were 101.5 males. For every 100 females age 18 and over, there were 92.9 males. The median income for a household in the city was $36,406, and the median income for a family was $48,929. Males had a median income of $37,000 versus $20,500 for females. The per capita income for the city was $18,949. There were 7.1% of families and 10.0% of the population living below the poverty line, including no one under the age of 18 and 10.3% of those over 64.
