The 2019 Spanish regional elections will be held on Sunday, 26 May 2019, to elect the regional parliaments of twelve of the seventeen autonomous communities—Aragon, Asturias, the Balearic Islands, the Canary Islands, Cantabria, Castile and León, Castilla–La Mancha, Extremadura, La Rioja, Madrid, Murcia and Navarre—, not including Andalusia, the Basque Country, Catalonia, Galicia and—for the first time—the Valencian Community.

715 of 1,208 seats in the regional parliaments will be up for election. The elections will be held simultaneously with local elections all throughout Spain, as well as the 2019 European Parliament election.

Election date

Determination of election day varies depending on the autonomous community, with each one having competency to establish its own regulations. Typically, thirteen out of the seventeen autonomous communities—all but Andalusia, the Basque Country, Catalonia and Galicia—have their elections fixed for the fourth Sunday of May every four years, to be held together with nationwide local elections.

In some cases, regional presidents have the prerogative to dissolve the regional parliament and call for extra elections at a different time, but newly elected assemblies are restricted to serving out what remains of their previous four year-terms without altering the period to their next ordinary election. In other cases—namely, Aragon, the Balearic Islands, Castile and León, Extremadura, Navarre and the Valencian Community—, the law grants presidents the power to call a snap election resulting in a fresh four year-parliamentary term. By the time of the 2015 regional elections, however, this prerogative had not yet been exercised by any of these communities.

Sources and further  reading:

https://europeelects.eu/2019/04/26/live-blog-2019-spanish-elections/

Andalucia.com

http://www.andalucia.com/spain/elections/home.htm