In 2015, 106 cities across the world participated on Open Data Day. This year, the Open Data Day is planned on 5 March 2016. Whether you are a developer who wants to create an application or a statistician, designer, librarian or citizen, everyone interested in Open Data is invited to participate.
The Open Data Day aims to stimulate the development of applications, publishing of data, creation of visualisations and publication of analyses using Open Public Data. The purpose is to show support for and encourage the adoption of Open Data policies by the world's local, regional and national governments.
To see which city is participating in your area, there is a specific Wikipedia page showing the city events that are currently planned. You can participate in one of the events listed there or even organise your own event.
Read more: http://opendataday.org/