Always start from known facts and work towards unknown information. For example, if the family Bible listed that a couple married at a specific church on a specific date, get that marriage certificate from the church. Getting the paper document from the church will quickly verify a known fact and familiarize the researcher with a church that might have been the place of worship for two families. Explore that possibility by checking members' lists, other weddings and baptisms, in addition to the graveyard. The family Bible most likely did not provide that much information. If the Bible was from the bride's family, it most likely did not list anything about the groom's family.
After exhausting the possibilities at the church, visit the courthouse in person or write a letter. If a marriage license or certificate was filed at the time of the wedding, additional information might be provided. Most courthouse marriage records will be indexed, so check for people with the same surnames as your couple. The amount of information in a wedding record differs over time. The earlier marriage records may provide much less information than more recent documents. Examine all the records available to get a complete picture of the family and its ancestors and collaterals.
Use common sense when searching for records of an event. When Joseph Cassidy was widowed in late 1882 certain events likely took place. He and his newborn probably moved to the apartment of his brother. Patrick and Ann Cassidy had a three-month old baby of their own and Ann likely nursed both girls. Joseph's daughter died in June 1883 at 506 West 14th Street. The 14th Street address was the home of her aunt and uncle. This makes sense that Joseph would move in with family, for a number of reasons. It provided his daughter a wet nurse. It provided a place for them to live and keep costs down instead of maintaining a separate household. It also provided Joseph the opportunity to continue to work and not need childcare.
Joseph is not in the city directory in 1884 or 1885. He did not re-appear until 1886. He was listed at 652 Second Avenue around East 35th Street. He moved several blocks north of his original residence. Patrick and Ann Cassidy, however, continue to reside in the original neighborhood until after the 1900 U. S. Census. Why would a widower without living children suddenly appear in a separate apartment? One likely answer is that he remarried. If he appeared in the 1886 city directory in a new neighborhood, consider that he remarried before 1886 and that he married closer to the older neighborhood before moving. He might have married in the new neighborhood, but marriages necessitate proximity. Make sure to exhaust the options of marriage locations near an original home before checking other locations. Search the civil marriage indexes but do not stop there if the wedding is not in the index.
Joseph Cassidy married his first wife at Immaculate Conception at 414 East 14th Street in 1878. Checking the parishes between East 14th and East 37th Streets proved fruitless for the second marriage. The marriage was not recorded with civil authorities and proved extremely difficult to find, writing to numerous parishes. His second daughter was born in Aug 1888 and baptized at the parish on St. Gabriel on East 37th Street. Her parents, however, were not married there.
Examine additional documents that may exist. New York City kept duplicate vital records from 1866-1888. A certificate was issued for each birth, death, and marriage recorded with the Department of Health. In addition to these certificates, which were forwarded to Albany, a register book was kept and retained locally. These one-line ledger entries were hand-written by a different person than the certificates and may provide a clearer view of the information recorded. The birth and death certificates have numbers that reference this register book.
Look at maps and master the local geography. Manhattan has a traditional grid pattern on much of its island. The streets increase numerically from south to north. The avenues increase numerically from east to west. It took years, but realizing that widowers in the 1880s probably did not set up their own apartments refocused the search. Instead of searching from where he was in 1882 to where he was in 1888, a search examined what parishes were close enough to his address on East 14th Street to marry his second wife. Finally, checking west of Manhattan's midway point at Fifth Avenue provided the elusive record. Joseph Cassidy married Ellen Hart on 20 December 1885 at St. Francis Xavier on West 16th Street between 5th and 6th Avenues.
Joseph and his second bride lived near each other but attended different parishes. Possibly she lived to the east of her church and he lived to the west of his. That would bring them close enough to meet but still reside in different parishes. The bride's church was where the wedding customarily took place. The lack of a civil marriage document can make finding a church record hard to find. Remember that just because it was not filed with the city does not mean the wedding did not take place or can't be objectively proven.
As you find documents new questions will be raised. Before finding Joseph's second wedding certificate, it was assumed that his second wife had been married before she wed Joseph. Their only known child was born in Aug 1888. This girl's birth certificate stated that she was the third child born to this mother and only one alive at the time. If there were no other burials in the Cassidy family grave between 1883 and 1889 when his second wife and daughter died, one assumed that Ellen's two earlier children must not be Joseph's.
The marriage record stated that she was Ellen Hart, which is the maiden name listed on her daughter's birth and baptismal certificates and Ellen's own death certificate. It is possible that Ellen had children out of wedlock or that she first married a man named Hart. These must be considered but more likely is that she bore two children to Joseph Cassidy in 1886 and 1887. They may have been twins and possibly stillborns. The church register should be checked thoroughly for any baptisms or burials. The vital records indexes should be checked for births or deaths of Cassidy children. It may turn out to be a clerical error on the part of the doctor, but further research should be conducted to determine if another, as yet unknown member of the family, served as a baptismal sponsor or provided a burial plot for the funeral.
The search will always continue for records but using a good deal of persistence and some common sense can lead to quicker success.