Sluggo, according to what Gail has unearthed, your question should have been, "where did the i
O.E. *willan, wyllan "to wish, desire, want" (past tense wolde), from P.Gmc. *welljan (cf. O.S. willian, O.N. vilja, O.Fris. willa, Du. willen, O.H.G. wellan, Ger. wollen, Goth. wiljan "to will, wish, desire," Goth. waljan "to choose"), from PIE *wel-/*wol- "be pleasing" (cf. Skt. vrnoti "chooses, prefers," varyah "to be chosen, eligible, excellent," varanam "choosing;" Avestan verenav- "to wish, will, choose;" Gk. elpis "hope;" L. volo, velle "to wish, will, desire;" O.C.S. voljo, voliti "to will," veljo, veleti "to command;" Lith. velyti "to wish, favor," pa-vel-mi "I will," viliuos "I hope;" Welsh gwell "better"). Cf. also O.E. wel "well," lit. "according to one's wish;" wela "well-being, riches." The use as a future auxiliary was already developing in O.E. The implication of intention or volition distinguishes it from shall, which expresses or implies obligation or necessity. Contracted forms, especially after pronouns, began to appear 16c., as in sheele for "she will." The form with an apostrophe is from 17c.
O.E. will, willa, from P.Gmc. *weljon (cf. O.S. willio, O.N. vili, O.Fris. willa, Du. wil, O.H.G. willio, Ger. wille, Goth. wilja "will"), related to *willan "to wish" (see will (v.)). The meaning "written document expressing a person's wishes about disposition of property after death" is first recorded c.1380.