Local elections in the United Kingdom are scheduled to be held on Thursday 2 May 2019, contesting about 270 English local councils, six directly elected mayors in England, and all 11 local councils in Northern Ireland. Additionally, there will be by-elections for a number of local authority seats.
Comprehensive information available here: https://en.wikipedia.org/wiki/2019_United_Kingdom_local_elections
This gives a list of seats with elections, including political history of those seats, plus information on where elections are not being held. For those that are not familiar with local election routines, some councils have all seats up for grabs, some a third (by rotation), and some none at all.