Is COVID-19 considered an act of god?

This is a great question.  Most contracts have a "force majeur clause."  This cause excuses parties from performing obligations when certain unforeseen and unavoidable events occur.  These are known as "Acts of God."  They generally refer to catastropic events, such as an earthquake, a war, etc.  And, your question is whether or not it applies to COVID-19.    There are currently tons of contract and insurance cases in Courts right to determine if the contract should pay the insurance based on whether or not COVID-19 was responsible.  For example, many restuarants purchased insurance policies for loss of business.  The insurance carriers did not predict the COVID-19 shut down, and now they do not want to pay for the loss of business, where they have been accepting the insurance payments from the restuarant for years.   Well, the same applies to you.  It is not your fault nor the venue's fault that your wedding cannot take place.  COVID-19 is an unforeseen event.  In my opinion, the "force majeur clause" should regard COVID-19 as an Act of God.  They probably do not want to give your down payment back, as they have lost so much business, they may not have the funds to do so.   Since this is only a down payment, you would probably qualify to take this claim to small claims court.  Let them know that you plan to sue them for the return of the down payment in small claims court.  If they do not pay you in a timely manner, file the claim in small claims court.  Good luck.