From Ballot Access News on December 9, 2019:
Four states hold their legislative elections in the odd year before presidential election years. The Libertarian Party had legislative candidates in all four of these states in 2019 (Louisiana, Mississippi, New Jersey, and Virginia), and polled the best vote it has ever received in this set of elections. It ran fifteen legislative candidates in 2019. The number of legislative candidates on the ballot in prior years: 2015 nine; 2011 twelve; 2007 twelve; 2003 five; 1999 five; 1995 five; 1991 four; 1987 one; 1983 two; 1979 eight; and 1975 six.
The 2019 Libertarian legislative candidates polled a total of 37,751 votes, the highest for any of this set of election years.
This blog post only concerns regularly-scheduled legislative elections, not special elections, which in most states can be held at almost any time.
The Libertarian Party is the only nationally-organized third party that had any legislative candidates in the regularly-scheduled 2019 elections.
Generally minor parties don’t exert much energy in these election years; there is too much distraction with the upcoming presidential election.