Mietje "Marie" Baron (5 February 1908 – 23 July 1948) was a Dutch swimmer and diver who competed at the 1924 and 1928 Olympics.

[2] Four years later she swam 3:15.2, but this was only enough for a silver medal, as her main rival Hilde Schrader clocked 3:12.6.

At the 1928 Games Baron also competed in the 10 m platform diving event and finished fourth.

[3] Between 1926 and 1928 Baron set four breaststroke world records, two in the 200 m (3:18:40 on 24 October 1926 and 3:12:80 on 22 April 1928) and two in the obsolete 400 m event (6:54:80 on 20 March 1927 and 6:45:60 on 25 November 1928).

[5] Next year she married Pieter Lourens de Puij.