This paper considers the degree and quality of Henry David Thoreau's self-professed mysticism, principally in his Journal, in which he uses the term and which features a representative and under-studied mystical experience. I begin by summarizing existing scholarship on the question of Thoreau's status as a mystic, highlighting important ideas to keep in mind and identifying scholarly shortcomings upon which to improve. I then move to the sites of Thoreau's most extensive use of the Chaldean Oracles, in his essay, "Walking," and A Week on the Concord and Merrimack Rivers, and the first notable instance of his association between mist and mystical thought. I conclude with the first five volumes of the Journal, leading to March 5, 1853, the date of Thoreau's self-designation as a mystic. Throughout the paper, my enquiry will proceed along three primary thematic lines—sense-experience, time, and reproducibility of observation—as considered in the motif of mist in the Journal.