On August 26, 1825, before the first session of the 19th Congress began, James Allison, Jr. (J) of Pennsylvania's 16th district resigned. A special election was held to fill the resulting vacancy.
Election results
Orr took his seat on December 5, 1825, at the start of the First Session of the 19th Congress
References
Pennsylvania's 16th congressional district special election, 1825 Wikipedia(Text) CC BY-SA