Which state was originally known as Columbia?

The state which was initially named as Columbia is Washington. The proposed name - the "Territory of Columbia" - was changed to "Territory of Washington" (honoring George Washington, the first president of the United States) in order to avoid confusion for the District of Columbia.

According to Wikipedia, "Agitation in favor of self-government developed in the regions of the Oregon Territory north of the Columbia River in 1851–1852. A group of prominent settlers from the Cowlitz and Puget Sound regions met on November 25, 1852, at the "Monticello Convention" in present-day Longview, to draft a petition to the United States Congress calling for a separate territory north of the Columbia River. After gaining approval from the Oregon territorial government, the proposal was sent to the federal government. The bill to establish the territory, H.R. 348, was reported in the U.S. House of Representatives by Representative Charles E. Stuart on January 25, 1853. Representative Richard H. Stanton argued that the proposed name—the "Territory of Columbia"—might be confused for the District of Columbia, and suggested a name honoring George Washington instead. The bill was thus amended with the name "Washington", though not without some debate, and passed in the House on February 10, passed in the Senate on March 2, and signed by President Millard Fillmore on the same day." More details here.