Not a church, but a former convent located next to the former St. Anthony's School, which can be seen to the right of this photograph. This convent included a chapel within it. It has not served as a convent for many years. This building is located one block from Our Savior's Lutheran Church, also depicted on this blog, and St. Mark's Episcopal Church is located on the next block, across the street from the school. The structure was built in 1954.
Postscript:
An article in today's Casper Star Tribune reveals that his building has been converted into luxury apartments, with no two being the same as no two rooms in the building were the same. It is presently at 60% occupancy. The developer, who owns the neighboring school, chose the name The Marian for it, recalling its role as a convent. The plan noted in the comments fell through, and he came up with this new one.
Date of original post: January 25, 2011.
Date of update: December 20, 2015.