Westphalia is a region of northwestern Germany and one of the three historic parts of the state of North Rhine-Westphalia. It has an area of 20,210 square kilometres and 7.9 million inhabitants. The territory of the region is almost identical with the historic Province of Westphalia, which was a part of the Kingdom of Prussia from 1815 to 1918 and the Freā¦Westphalia is a region of northwestern Germany and one of the three historic parts of the state of North Rhine-Westphalia. It has an area of 20,210 square kilometres and 7.9 million inhabitants. The territory of the region is almost identical with the historic Province of Westphalia, which was a part of the Kingdom of Prussia from 1815 to 1918 and the Free State of Prussia from 1918 to 1946. In 1946, Westphalia merged with North Rhine, another former part of Prussia, to form the newly created state of North Rhine-Westphalia. In 1947, the state with its two historic parts was joined by a third one: Lippe, a former principality and free state.