A recurring bit of Texas mythology and misinformation is that Texas is the only state that was a Republic before it joined the Union. This simply is not true.
The Republic of Vermont existed for fourteen years, from January 15, 1777 to March 4, 1791. Vermont was the first state to enter the Union that had not been part of the the original thirteen colonies.
For nine years, the Republic of Texas existed, from March 2, 1835 to December 29, 1845.
California existed as a Republic for twenty-nine days, from June 14, 1846 to July 9, 1846.