I’m trying to find out anything about my grandmother side of the family her name was Margaret Costello she married John A Allen in nineteen twenty and had three children Reginald Marj and Margaret thank you Ivan

In the 1939 Register there are John A Allen (born 26 Oct 1898), Margaret Allen (born 11 April 1901) and Reginald Allen (21 December 1920). Their address is 43 Don Rd.

In the Burial Records to the left here are John Arthur Allen 1947 and Margaret Allen 1956 of 43 Don Rd who share the same plot at City Road cemetery.

www.freebmd.org.uk has an index of marriages etc.
It includes this which may be your family:
Marriages June quarter 1920)
Costello Margaret Allen Sheffield 9c 1293
Marriages June quarter 1920
Allen Arthur Costello Sheffield 9c 1293 (note forename)

The Parish Records to the left have a transcription of the marriage record. It includes the fathers names and witness names.

In 1939 in the household was also Marjorie Allen, name changed to Crutchley born 21 January 1927.

Some family trees at Ancestry say that Margaret Costello was born in Ireland. The 1939 register says the birth day was 11 April 1901. The marriage record says the father was James Costello.

The May 1920 marriage record says Margaret was age 19 which supports a birth around 1901. And Arthur was 21.

The January 1956 burial record says she was 54 also supporting birth 1901.

https://www.irishgenealogy.ie/en/ is the top place to search after registrations started there. I can't find a Margaret Costello with a matching birthday 1900-1902.

Her father was James and her birthday was 11 April. Consider the following possibility:
Margaret Costello born 11 April 1899, registration Balla, Castlebar, Father James Costello, Aughalisha, mother Catherine Costello, formerly Costello.

This could be that family in 1911:
http://www.census.nationalarchives.ie/pages/1911/Mayo/Bellavary/Aghalusky/711603/

James Costello was a marriage witness. There was also a James age 5 in this 1911 household (could a 14 year old be a marriage witness?).

I'm not saying this is your Margaret, but that it may be a possibility. Her information about her birth year could be hazy.

I wish to withdraw the previous message. That Margaret went to USA.
Shouldn't there be a 1 hour delete/amend?

When Margaret Costell married John Allen, her address was given as, 72 Swarcliffe Road.

On the 1911 census at 72 Swarcliffe Road, Sheffield, there is:
Edward Costello,40yrs, coal miner hewer, born Ireland. With him is wife Martha 34yrs, son James 16yrs, son Thomas 14yrs, dau MAGGIE 9yrs, son William 6yrs, son Edmond 3yrs and dau Nellie 1yr.
From Martha down to William born Eckington. Edmond and Nellie born Darnall.

In 1901 the family are living at Pinfold St, Eckington. But Edward has now become Edmund.

Birth Reg: Margaret Costello, Q2 1901 Chesterfield, Dby. MMN Sherlock.

1881 Back Lane, Eckington,Dby.
Patrick Shirlock, 40yrs, coal miner, born Ireland.
Wife Mary 30yrs, dau Mary 6yrs, dau MARTHA 3yrs and son Thomas 1yr.
All the rest of the family born Eckington.
In 1891 The family ar at North Gate, Eckington, and Mary is now a widow.

Patrick Sherlock married Mary Alcock Q2 1869, Chesterfield Reg. District.
Patrick died in 1888 aged 48yrs.

In 1861 the Sherlock and Alcock families are both in Eckington.

Moira.

Further confirmation of Moiras find
1921 census Shirland Lane, Margaret Allen b 1901 with husband John Arthur and newborn son Reginald
Margaret birthplace Eckington Yorks.
Dave

In the Sheffield and Rotherham Independent, 22 July 1886.
Accident at Renishaw Colliery.
Patrick Sherlock residing at 20 Northgate, Eckington, met a serious accident. He was
removing props when a quantity of stone fell on him, injuring his back and crushing him.
He was conveyed home in the companys ambulence.

Presumably this was the cause of his early death in 1888.

Moira.

Father is Edmond for Martha's 1938 marriage
COSTELLO, Martha (Spinster, age 25, ~, residing at 72 Swarcliffe Rd).
Married George Leslie STUBBINS, on January 1, 1938, by Sydney T G Smith (Banns) at
Christ Church, Attercliffe. Father's name is Edmond Costello, deceased (Coal miner).
Married in the presence of John Henry Greaves, Dorothy Stubbins.

But Margaret's father at her marriage is James. Could be transcription error or maybe the writer got it wrong.

https://www.gro.gov.uk/ births index
COSTELLO, MARTHA mother's maiden name SHIRLOCK
GRO Reference: 1912 M Quarter in SHEFFIELD Volume 09C Page 1481
This confirms Moira's Shirlock/Sherlock link.

Which takes us back to Margaret
COSTELLO, MARGARET SHERLOCK
GRO Reference: 1901 J Quarter in CHESTERFIELD Volume 07B Page 831

Others:
COSTELLO, JAMES COSTELLO SHERLOCK
GRO Reference: 1895 M Quarter in CHESTERFIELD Volume 07B Page 814

COSTELLO, KATE SHERLOCK
GRO Reference: 1899 J Quarter in CHESTERFIELD Volume 07B Page 845

COSTELLO, WILLIAM SHERLOCK
GRO Reference: 1904 D Quarter in OF CHESTERFIELD Volume 07B Page 808

COSTELLO, EDMUND SHERLOCK
GRO Reference: 1908 M Quarter in SHEFFIELD Volume 09C Page 706

COSTELLO, ELLEN SHARLOCK
GRO Reference: 1910 M Quarter in SHEFFIELD Volume 09C Page 663

https://www.freebmd.org.uk/
Marriages March quarter 1895
Costello Edmund Chesterfield 7b 854
Mullarky Edward Chesterfield 7b 854
Schofield Clara Chesterfield 7b 854
Sherlock Martha Chesterfield 7b 854

Hello I’m Ivan Allen thank you very much I’m Margaret and Johns oldest grandson so I was told I didn’t know my grandfather as I was born in 1947 the year he died and I didn’t see my grandmother much but I didn’t know what happened to the family but I think that there son was having an affair with him and she was married to Johns brother and his name was called Reginald Allen the Allen family lived on Norman street Atterclffei didn’t find anything out till my mother died and I find some letters from her that was the first I new about them I still to this day how many aunts and uncles I have it just ripped the family’s a part And heard a rumour that James Costello her father was in the I R A in Ireland Margaret and John had three children the youngest one choked on something and died her name was Margaret as well thanks for your help you told me more than I ever know thanks Ivan