In 1895, Grabski married Ludmiła Rożen. The couple had five children – three daughters (Feliksa, Ludmiła, Janina) and two sons (Stanisław and Zbigniew). Stanisław died in 1920 during the Polish-Soviet War. Zbigniew (1907–1943) was a scoutmaster, jailed until 1941 by Soviets, he died as a result of an accident during his military duties. After the death of his wife in 1915, Stanisław Grabski married Zofia Smolikówna in 1916. They had two daughters – Anna (born 1919) and Stanisława (1922–2008).
