Five states will hold the final state legislative primaries of this election season on Tuesday, with some of the most closely watched state chambers among them.

With the exception of half of the Delaware Senate, all seats are up this fall in both chambers in Delaware, Massachusetts, New Hampshire, New York and Rhode Island. While primaries will be held in all five states, among the most scrutinized will be those for the New Hampshire House and the New York Senate, where a splinter group of Democrats has complicated the party’s majority rule in recent years. In late 2012, a handful of Democrats identifying as the Independent Democratic Conference entered a power-sharing agreement with the GOP, denying the Democratic Party majority rule, though they reconciled in June.

“Those may be the most interesting primaries of any state this year,” says Tim Storey, an expert on state legislatures with the bipartisan National Conference of State Legislatures. Of the 63 New York Senate seats, 20 feature incumbent candidates running unopposed, according to data maintained by Ballotpedia, an online political encyclopedia.

State legislative seats have gained heightened prominence in recent years, as Congress has grown gridlocked and legislatures have increasingly fallen under unified party control. With just three divided states, the number of legislatures with single-party control is at its highest level in 70 years.

New Hampshire is one of those three states with different parties in control over each chamber, but that could change this fall if Republicans can win back the House, Storey says.

All told, there are 1,001 open seats in the five states hosting primaries on Tuesday, according to Ballotpedia, but candidates for 301 of those seats are running unopposed as of Monday.

That reflects a nationwide trend. Of the nearly 7,400 legislative seats nationwide, roughly 6,050 are up for election or reelection this season. About 1 in 3 of them feature an unopposed candidate, virtually all of them incumbents. Four states — Louisiana, Mississippi, New Jersey and Virginia — are not holding legislative elections this year.

CORRECTION: An earlier version of this post left Virginia off the list of states not holing legislative elections this year.