Trinity County is one of the original 27 counties. It was administered by Shasta County until 1851. It takes its name from the Trinity River, named in 1845 by Major Pearson B. Reading, who was under the mistaken impression that the stream emptied into Trinidad Bay. Trinity is the English version of Trinidad. Territory which at one time was in Trinity County is now in Del Norte, Humboldt, and Siskiyou Counties.

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