Jeronimas Pleckaitis (10 December 1887 in Keturvalakiai, Russian Empire – 29 October 1963 in Pilviškiai, Lithuanian SSR) was a Lithuanian politician.
He was a member the national parliament, the Seimas, from 1920 to 1927, representing the Social Democratic Party of Lithuania.
After the military coup d'état of December 1926, Pleckaitis became an active member of the opposition to President Antanas Smetona and Prime Minister Augustinas Voldemaras.
He participated in the failed Taurage Revolt in September 1927 and fled abroad to avoid arrest.
He organized a group of men, known as pleckaitininkai, that received assistance from Poland and continued to plot against the Lithuanian government.
He was arrested by the German police in September 1929 and sentenced to three years in prison.
He was arrested again by Lithuania in 1940.
In 1944, he was arrested by the Soviet authorities and sent to a Gulag camp in the Tyumen Oblast.