[2] Per Japanese census data,[4] the population of Koga peaked around the year 2000 and has declined slightly since.

During the Muromachi period it was the location of the Koga kubō, a secondary government created by the Ashikaga shogunate to rule eastern Japan.

Koga has a mayor-council form of government with a directly elected mayor and a unicameral city council of 24 members.

In terms of national politics, the city is part of Ibaraki 7th district of the lower house of the Diet of Japan.

At present, the economy is highly industrialized, with the number of factories as second within Ibaraki Prefecture, after Hitachi city.