National Mills Day

{{Use British English|date=October 2014}}

{{Use dmy dates|date=April 2020}}

{{Infobox holiday

| holiday_name = National Mills Weekend

| image = File:Herringfleet Smock Drainage Wind pump - geograph.org.uk - 1919532.jpg

| caption = Herringfleet Windmill in Suffolk, open to the public on National Mills Day

| type = secular

| observedby = United Kingdom

| longtype = Opening wind and watermills to the public

| week_ordinal = second

| weekday = Saturday

| month = May

| duration = 2 days

}}

National Mills Day is an event in the United Kingdom. It occurs annually on the second Sunday in May. It started off as a single day event,{{Cite web|last=|first=|date=|title=UK National Mills Day 1998|url=http://www.windmillworld.com/uk/millsdaypast.htm#1998|archive-url=|archive-date=|accessdate=5 June 2009|website=|publisher=Windmill World}} but expanded to include Saturday as well as Sunday, and is now promoted as National Mills Weekend. The event is coordinated by the Wind and Watermills section of the Society for the Protection of Ancient Buildings.{{Cite web|url=http://www.windmillworld.com/uk/millsweekend.htm |title=National Mills Weekend |publisher=Windmill World |accessdate=5 June 2009}} Traditionally, many preserved wind and watermills that are usually closed to the general public open their doors and offer an insight into the mill workings and history.

In support of National Mills Day, Denby Dale Radio Club coordinates hundreds of amateur radio stations who operate from alongside and sometimes inside the mills.