A late 19th-century Tiffany window that has illuminated a Connecticut church for the past 125 years could fetch $2 million when it headlines the Christie’s design sale at Rockefeller Center in June.

The two-lancet scene, long set above the balcony of Second Congregational Church in the town of Winsted, depicts an idyllic landscape at sunset. In the foreground, a staggered waterfall’s streaky glass lends it froth and shimmer with surrounding palms reaching into a sky bruising to night. The right-hand lancet, backgrounded by a streak of purple mountains, is alive with a burst of lilies and irises.

The window, which is topped by a medallion featuring a crown of hand-cut jewels, was commissioned by Ellen Wright Boyd in memory of her parents, John and Emily Boyd , and installed in 1899. John Boyd, a former Secretary of State of Connecticut, made his fortune as a steel industrialist and is best known locally for his history of the region’s early settlers.…