Ernst Jans Koster, born in Franeker on August 1, 1816, son of Jan Bernardus Koster and Klaske Jans Groeneveld, died in Harlingen on April 10, 1862, aged 45 years.

Ernst was married in Franeker on May 14, 1837, at the age of 20 to
Trijntje Willems Geldersma (aged 24 years), born in Franeker on September 5, 1812, daughter of Willem Pieters Geldersma and Aafke Pieters Vlietstra, died in Harlingen on January 25, 1902, aged 89 years.

• 1 : Jan Koster, born in Franeker on June 18, 1840, painter's man, died in Harlingen on February 23, 1918, aged 77 years.
  Jan was married in Harlingen on May 17, 1866, at the age of 25 to Elisabeth van der Wijk (aged 24 years), born in Harlingen on February 4, 1842, daughter of Jan Jans van der Wijk and Gerritje Foppes Molenaar, died there on January 15, 1890, aged 47 years.