William "Duff" Armstrong

William "Duff" Armstrong (1833–1899) was a defendant in an 1858 murder prosecution in which he was defended by Abraham Lincoln, then-future President of the United States. The case would later be portrayed in the 1939 film Young Mr. Lincoln.

• Robert Armstrong (1760–1834), married on June 22, 1787, Nancy Green Armstrong (1768–1856), daughter of George William Green (1725–1770) and Nancy Ann Justice (1730–1774). Prior to marrying Robert, Nancy had one son, Bowling Green (1786–1842), m. Nancy Potter Green (1793–1867). Bowling Green had eight children. Robert and Nancy Armstrong had several children:
  • Rhoda Armstrong Clary (1794–1840), m. John Clary (1793–1860). They had nine children.
  • Hugh Armstrong (1800–1839), m. Francis Graham Greene (1809–1881). They had five children.
  • John Jack Armstrong (1803–1854), married Hannah Jones (1810–1890), daughter of John Jones (1776–1845) and Lydia Gum Jones (1777–1858). Hannah Jones Wilcox married in 1862 Samuel Wilcox (1812–1870). Hannah Jones Armstrong Wilcox had two brothers and one sister.
    • Corporal Pleasant Carwin Armstrong (1829–1863), married on May 22, 1860, Martha E. Schults (1843–1882). Died in the Civil War.
      • Hugh Armstrong (1861–1917), married Ida J. Wallace (1863–1962), daughter of William Wallace and Raye Warnock Wallace.
        • Paul R. Armstrong (1893–1948)
    • William Duff Armstrong (1833–1899), married on April 18, 1864, Martha E. Schults, the same as above.
      • Hannah Armstrong Munsch (1865–1936), married Joseph Munsch (1860–1944).
        • Robert Wayne Munsch (1895–1901)
      • John Crittenden Armstrong (1868–1871)
      • Robert W. Armstrong (1871–1920)
      • Julia A. Armstrong (1876–1878)
    • James A. Armstrong (1838–1879), married Margaret J. Ishmael (1844–1934) on October 15, 1863
      • Samuel D. Armstrong (1865–1912), married Polly Ann Armstrong (1866–1935) on October 4, 1885
      • Mary Blanche Armstrong (1877–1891)
    • Robert Armstrong (1852–1906), married Martha Wilcox Armstrong (1856–1937), daughter of Samuel Wilcox (1812–1870) and Rachel M. Rogers (1831–1860)
      • Sylvia Armstrong Smith (1874–1960)
  • Elizabeth Betsy Armstrong Potter (1805–1886), m. Edward Bunn Potter (1795–1863). They had nine children.
  • Nancy Armstrong McHenry (1809–1894), m. Henry McHenry (1802–1881). They had three children.
  • Eliza W. Armstrong Pantier (1812–1848), m. David Marion Pantier (1808–1889). They had six children.

Armstrong was charged with the August 29, 1857, murder of James Preston Metzker in Mason County, Illinois. His father, Jack Armstrong, had been a friend of Lincoln while he was studying law in New Salem, Illinois. When Lincoln heard of the murder charge, he wrote to Jack's widow, Hannah, and volunteered his legal services pro bono. The trial was moved to Cass County and held at the courthouse at Beardstown, Illinois.

Witness Charles Allen testified that he saw Duff Armstrong strike Metzker with a slung shot. Under cross-examination, Lincoln pushed for further detail and Charles Allen testified that he was at a distance of 150 feet, but could clearly see the act by the light of the full moon. Abraham Lincoln used judicial notice, then a very uncommon tactic, to show Allen lied on the stand when he claimed he had witnessed the crime in the moonlight. Lincoln produced an almanac to show that the moon on that date could not have produced enough light for the witness to see anything clearly. Based on this evidence, the jury acquitted Armstrong after only one ballot.

Armstrong went on to join the Union forces in the American Civil War. He became ill in 1863 and, at his mother's request, Lincoln arranged for Armstrong's discharge. Armstrong lived long after the war; his death was reported in the New York Times on May 14, 1899.

William Duff Armstrong is buried in the New Hope Cemetery in Mason County, IL. A plaque is erected at his gravesite which reads, "WILLIAM DUFF ARMSTRONG accused slayer of Preston Metzker, May 7, 1858 freed by Lincoln in Almanac Trial".