(Duncan, 35', 1882, IA-15-05) E. of Atlantic, Grove Township, Cass County, IA. US6 E. 2.1 miles from jct with IA83 (Poplar St.) in Atlantic, N. on 635th St. 0.5 miles to the house on the W. side of the road at 56711 635th St., just N. of Galveston Rd. (4-28-04, N41° 24.690', W94° 58.500')