The U.S. state of West Virginia has 55 counties. Fifty of them existed at the time of the Wheeling Convention in 1861, before which West Virginia was part of the state of Virginia. The remaining five (Grant, Mineral, Lincoln, Summers and Mingo) were formed within the state after its admission to the United States on June 20, 1863. At that time, Berkeley County and Jefferson County, the two easternmost counties of West Virginia, refused to recognize their inclusion in the state. In March 1866, the United States Congress passed a joint mandate assenting to their inclusion.