The Mullen or Willow Church was located in Section 23 of Willow Township, five miles south and one mile east of Charter Oak, Iowa. It was served by pastors that lived in the community from 1883 to 1918 when it became a Methodist Church and was a circuit charge with Charter Oak and Ute. Sunday School was held in the morning and church service in the evening.

In 1944, the church merged with the Charter Oak Methodist Church. The Willow Church was sold to Mr. and Mrs. Ben Klinker who dismantled it and used the lumber to build a new house on their farm. The money from the sale of their church building was added to the building fund of the Charter Oak Methodist Church.

Some of the families that attended sunday school and church there were: E. E. McElwain, A. L. Dietz, Ward Sterrett, George Weiss, Frank Larson, Arno Steffen, A. J. Ahart, John Jensen, Henry Hanson, Nels Nelson, Chris Brink, Tom Hodkin, William Keim, Ed Keim, A. C. Wickwire, Charles Weed, Ed Reinking, Arnold Schmidt, Wilbor Hall, Shorty Miller, George Specht, Oscar Harden, Vernon McElwain, and Clarence Weiss.

Some Ministers that served the church were: Rev. A. J. Barkley, Rev. E. M. Cathcort, Rev. C. N. McMillan, Rev. G. J. Poppenheimer, Rev. H. C. Travis, Rev. George E. Scheider, Rev. W. F. Lane, Rev. G. M. Squires, and Rev. L. A. Hunsley.

The Sunday School was always one of the most active and vital departments of the church. Epworth League, an organization for young people, was also very active. The Ladies Aid was also an active group in the church.

Source: The 1991 Charter Oak centennial book.