*Belfast, Northern Ireland
Den Bosch, Netherlands
The Hague, Netherlands
*Loughbrickland, Northern Ireland
Brussels, Belgium (referendum night)
Washington DC, USA
Portland OR, USA
Morchard Bishop, England
Chicago IL, USA
That's 28, the same as last year's record high, in 14 different countries.
However I have also changed planes in Vienna, Istanbul, Warsaw, Rome, Ljubljana, Stockholm and Copenhagen, and driven through Luxembourg, so my total number of countries visited for the year is a record 22 (last year was 21).
Edited to add: Of course, the day after I posted this, I was sent to Strasbourg for three days and two nights. So my total for 2016 was 29, making 2016 a record year both for different overnight stays and for countries visited.
Previous years: 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015
That's all the places where I have checked in with Swarm so far in 2016. Most of my travel has been in the northwestern corner of Europe.