Holbeach on Wikipedia.
 

All Saints. Another view, four of the interior - 1, 2, 3, 4, three of the superb tomb of Sir Humphrey Littlebury, who died in the late 14th century - 1, 2, 3, and the handsome font. TF 3591 2479. All © David Regan (2019 and 2020). Link. Grade I listed.

The Baptist Church of 1845 stands on Albert Street at TF 3601 2476. © David Regan (2020). Link. Grade II listed.

Holy Trinity (R.C.) on Foxes Low Road. © David Regan (2019). Link.

The Methodist Church is on Albert Walk and Albert Street. Its predecessor, built as United Free Methodist, is marked on the same site on the 1903 6" O.S. map, and an old postcard showing it is available here (the first image, click to see an enlargement, chapel on right side of the road). TF 3598 2466. © David Regan (2020). Link.

Mortuary Chapels (1854) in Park Road Cemetery. TF 3620 2508. © David Regan (2019). Link. Grade II listed.

The 6" O.S. map of 1906 marks a chapel on Edinburgh Walk at TF 3630 2486. The 25" map of 1904 labels it as Primitive Methodist. The My Primitive Methodist entry for Holbeach P.M. Chapel has it opening in 1834, but doesn't know the chapels location. A Streetview stroll along Edinburgh Walk fails to find any obvious trace of it, so it's safe to assume it has been demolished. I think the site is now occupied by the building behind the lamp-post here on a 2010 Streetview. It can just be seen in the background on this old postcard here (4th row, last image on the right, behind and to the right of the large building), and better seen here (though this link may not remain active).

Another Chapel marked on the same map stood on Chapel Street at TF 3606 2478. I'ts denomination isn't marked on any maps available to me, but this source says it was Wesleyan, of 1808. Now demolished, it stood under the shop and its adjacent access area seen here, © David Regan (2020).

Another Chapel stood on Park Road at TF 3591 2488. This may be the Congregational Church of 1870 mentioned on Genuki here. The building survives, in commercial use, and can be seen in a 2011 Streetview.