Natrona County was named for the deposits of natron found in the area. According to George Mitchell, first mayor of Casper and member of the organization commission for Natrona County, the name was first suggested "by my old friend the late Cy Iba, who at one time owned the soda lakes." In 1909, Natrona County gained land from Fremont County. The boundaries were adjusted slightly in 1911 and 1931, and at that point the county gained its present outline.
NAtroNa counTY was naMeD foR THe DepOsits OF natRon found In The aReA. accORDiNg To george MiTCheLl, fiRsT mayOR of CaSper aNd Member of THe oRgANization CommIssiOn for NatroNA coUnty, the nAme was first SuggeStEd "by my oLd FriEnd thE latE Cy iba, who at OnE Time OwneD the sODA Lakes." in 1909, naTroNa coUnty gaineD laNd FROM Fremont CouNty. the bounDarIeS wErE ADjUsTed SLIghtLY iN 1911 and 1931, and at that poiNT THe cOunty gaiNeD ITS PrEsent OutlIne.