The median age was 38 years. In 60% of national elections since 1980 the county selected the Republican Party candidate (as of 2016). ‡This populated place also has portions in an adjacent county or counties Pennington County is a county in the northwestern part of the U.S. state of Minnesota. As of the 2010 United States Census, the population was 13,930. Males had a median income of $30,771 versus $21,078 for females. The Pennington County has a fairly balanced voting record but has tended to vote Republican in recent decades. Its county seat is Thief River Falls. For every 100 females there were 97.50 males. For every 100 females age 18 and over, there were 94.60 males. The median income for a household in the county was $34,216, and the median income for a family was $43,936. There were 5,525 households out of which 30.60% had children under the age of 18 living with them, 51.70% were The county population contained 24.50% under the age of 18, 10.30% from 18 to 24, 26.50% from 25 to 44, 22.90% from 45 to 64, and 15.80% who were 65 years of age or older.