In 1926 it was again necessary to provide more space for the growing church. This was accomplished by excavating the basement to make the Lewis Room, which was dedicated December 12, 1926.
On Palm Sunday, April 10, 1927, mortgages of $2,500 on the Main Street parsonage and $1,000 on the church were burned at the morning worship service. This was the first time in more than twenty-five years that the church property had been mortgage free.
During the week of November 17-24, 1929, Old South celebrated its sixtieth anniversary. President Daniel Marsh of Boston University gave a special address on November 24th.