Castle Douglas on Wikipedia.
 

Brethren Hall (2021 Streetview) on Academy Street. NX 7667 6230. Link - dates it to 2014, moving here from a building on St. Andrew's Street, so far unidentified.

St. Ringan, the parish church on Queen Street. Originally a Relief Church of 1803, its convoluted history can be seen here. NX 7655 6221. © Bill Henderson. Link.

Elim New Life Church on Blackpark Road, as seen by Streetview in 2021. NX 7604 6216. Link.

Old maps show a Free Church on Queen Street at NX 7647 6233. It's called St. George here, where it's dated to 1865 (successor to one on Cotton Street), closing at some point after 1923. The bank on its site was seen by Streetview in 2021. The Cotton Street Free Church is shown on a map of 1853 at NX 7643 6243. Its site (roughly the garden) was seen by Streetview in 2021.

This source says that the end terrace house on Queen Street seen here by Streetview in 2009 was, in the 1960's, a Gospel Hall. NX 7660 6237.

According to their website, the local Quakers meet in Bowlers Hall on Cotton Street. It was seen by Streetview in 2021. NX 7622 6222. A previous meeting place is given here as the Community Centre on Cotton Street, seen by Streetview in 2009.

The former St. Andrew (which was the parish church) on Marle Street and Lochside Road, converted into a theatre in the 1990's. This source dates it to 1868-1991. NX 7639 6197. © James Murray (2009). Category C listed.

St. John's R.C. Church (2021 Streetview) shows on the 1895 25" O.S. map on Abercromby Road. It's dated here (which calls it St. John the Evangelist) to 1867-8 to the 2000's when it was closed because of structural problems. It also says that the congregation continues, meeting at St. Ninian's (q.v.). NX 7625 6232.

St. Ninian (Episcopal) on Whitepark Road, as seen by Streetview in 2021. NX 7657 6195. Link1. Link2 dates it to 1856-61, and says it used to have  spire, taken down in 1950. Category B listed

Trinity Houses (2021 Streetview) on Abercromby Road is the former Trinity United Free Church. This source dates it to 1870, replacing an earlier church on a different site, and closing in 1923. NX 7622 6238. The earlier church shows as United Presbyterian on a map of 1853 further N.W. along Abercromby Road at NX 7615 6249. In a 2021 Streetview the church would have stood in what is now the garden, long axis parallel to the road, near the wall. Link dates it to circa 1820.