Miss. Code Ann. § 19-1-47

Harrison County is bounded by beginning at the southeast corner of section twenty-one, township four, south, range nine, west; thence due south through the middle of said range nine to the middle of the Bay of Biloxi; thence along the middle of said Bay of Biloxi to its entrance at the east end of Deer Island; thence due south to the southern boundary of the State of Mississippi on the Gulf of Mexico; thence westwardly along said boundary to a point from which a line due north strikes the middle of the Bay of St. Louis; including all the islands within six leagues of the shore of the Gulf of Mexico; thence due north to the entrance of said bay; thence along the middle of said Bay of St. Louis northwardly to a point from whence the point at which the line between ranges fourteen and thirteen comes to said bay bears due north; thence due north to the southwest corner of section thirty-one, township four, south, range thirteen, west; thence east to the southeast corner of section thirty-six, township four, south, range thirteen, west; thence north to the northeast corner of section twenty-five, township four, south range thirteen, west, thence east to the point of beginning. The county sites are Gulfport and Biloxi.