Margaret Cornett, who chaired a committee that has planned yearlong celebrations to commemorate the milestone, said the two congregations have had remarkably few disagreements over the years.
When church leaders considered splitting in the 1960s, Cornett said they roundly rejected it.
"We didn't want to do it," she said. "It would have meant that one congregation would have had to buy out the other."
Instead, church members said the congregations have drawn closer together over the years. The Lutheran Service is at 8:15 a.m. and the United Church of Christ worships at 9:45. In between, they conduct a joint Sunday school.
And whenever there is a special event, church members added, they are nearly always combined.
The church formed in 1747 in a log cabin near the Conococheague Creek, Cornett said. The two congregations moved to the present site in 1795. In 1897, the old structure was torn down to make way for the current building, Cornett said.
In the early days, a traveling minister would cross the Conococheague and preach to both congregations, Cornett said.
"Sometimes it was up and very dangerous," she said.
McCarter said the original church building doubled as a fort, which also brought the congregations together.
"Whether you were Lutheran or a member of the United Church of Christ, you went there if you didn't want to be attacked by Indians," she said.
Today the roughly 240 Lutherans and 200 United Church of Christ members have far more similarities than differences. The major difference in the religious service focuses on the role of communion, said the Rev. Mary Amundson, the Lutheran pastor.
Amundson said Lutherans take communion more frequently.
Amundson pointed out that the committee that organized the celebration had three members from each congregation.
"They invited me to come and say a prayer, but they did all the work," she said. "That's really a sign of why the congregations have worked together for 250 years."