Cathedral of St. John in the Wilderness, Episcopal cathedral in Denver, United States.

The Cathedral of St. John in the Wilderness is a limestone Gothic Revival church at 14th and Washington in Denver, Colorado. Only the nave was completed, measuring 185 feet long, 52 feet wide and 65 feet high, with a temporary brick chancel. The original plan by Tracy and Swartwout called for flying buttresses, two transepts, a choir and a great tower, none of which were built.

An earlier church at a different site in Denver burned down in 1903, which led the congregation to begin work on the current building around 1909. During construction, problems with the foundation required changes to the original design before the work could continue.

The name "in the Wilderness" comes from 1860, when the parish's nearest Episcopal neighbour was 700 miles away in Kansas. Its first dean, H. Martyn Hart, helped found the Denver Charity Organization in 1887, the country's first community charity solicitation fund, later renamed the United Way. Justice Byron White was buried here in 2002.

The cathedral stands at 14th Avenue and Washington Street in Denver, at the edge of the Capitol Hill neighborhood. The entrance is on Washington Street, and the nave is reached by a short flight of steps. The interior is open during daylight hours, and weekday visits are usually quieter than Sundays, when services draw a regular congregation.

The cathedral's two transepts, choir and great tower were designed but never built; only the limestone nave was completed, with a "temporary" brick chancel that still stands. The ceiling of the nave rises 65 feet over a space 185 feet long and 52 feet wide.