The countries have told UEFA that they would be interested in bidding to host the European Championships on a three-way basis. Beforehand, only Turkey had informed UEFA that they wanted to host the tournament.
A source close to UEFA has confirmed to the Press Association that a written expression of interest from the three 'Celtic' countries has been submitted to the European governing body. Any other declarations of interest must be submitted by midnight on Tuesday.
Bidders would need to put forward up to 10 stadiums to host matches in the European Championships, which is being expanded from 16 teams to 24 from 2016.
Scotland and Wales would struggle to provide that number of stadiums to satisfy UEFA requirements but Ireland's involvement would cover the shortfall.
The formal declaration of interest does not commit the Celtic countries to proceeding with a bid, however - a decision is not due to be taken by UEFA for 18 months.
The countries have not fared well in the past in bidding for the tournament. Scotland and the Republic of Ireland bid jointly for Euro 2008 but were one of the first to be eliminated, and Scotland and Wales considered bidding jointly for Euro 2016 but decided against it.
Turkey's bid is in some disarray already because their FA has been engulfed by allegations of corruption and match-fixing in Turkish football, and it also conflicts with Istanbul's bid to land the Olympics in the same year.
UEFA president Michel Platini had signalled he would support Turkey's bid, but only if Istanbul fails in its effort to host the Olympics.
With the deadline to express an interest approaching, Georgia said it would go it alone with a bid, ditching an original plan to co-host with Azerbaijan after Baku withdrew its interest in order to focus on a bid for the 2020 Olympics.
Georgia would have to build a number of new stadiums and the country's sports minister detailed its plans on Tuesday after confirming that a formal expression of interest had been sent to UEFA.
Construction of a new stadium in the Black Sea resort of Batumi would start this year, with further new stadiums planned for Gori, Ozurgeti and Zugdidi and major overhauls of stadiums in Tbilisi and the country's second largest city of Kutais, Lado Vardzelashvili told a televised news conference.
Local news agency www.vivil.ge reported that the country's largest stadium, the Boris Paichadze National Stadium, has a capacity of 55,000 with Tbilisi's Mikheil Meskhi Stadium currently holding 25,000.
UEFA requires at least two stadiums of 50,000 seats; three of 40,000 and four of 30,000.