Official notification of their ceremony was displayed at Maidenhead Town Hall outside London, alongside the other impeding weddings and partnerships.
Local council leader Mary Rose Gliksten says they're working with police to manage the crowds that are expected to show up.
"Sir Elton and Mr. Furnish are making a solemn and formal commitment to each other, and our Guildhall offers them dignity and privacy," Gliksten said earlier this week.
When the pop star announced the couple's plans last month, he said it would be "a very small family affair."
"The ceremony itself will be David's parents and my parents and the two of us," John told Attitude magazine. "Out of respect for their support, we want to just keep it small. Not to make a ballyhoo of the ceremony."
Furnish, a Canadian-born filmmaker, and John have been together for 12 years.
Dec. 21 is the when a new British law becomes in effect. Passed last year despite some opposition from Parliament's unelected House of Lords, it permits civil ceremonies that will give same-sex couples the same social security, tax, pension and inheritance rights as married couples.