From Michigan Place Names
HEMLOCK, Saginaw County: Philo Thomas became the first settler here in 1865, followed by John Codd in 1866. W. S. Gillespie built a sawmill here in 1868, and soon after, the Saginaw Valley & St. Louis Railroad came through from Saginaw, bringing an influx of settlers. Given a post office as Hemlock City on May 24, 1869, with Jacob King as its first postmaster, the name being shortened to Hemlock on March 27, 1895. named from the vast number of hemlock trees which covered the area [Mary C. Rauchholz; Mills; PO Archives] .