Houses were moved frequently in the 19th and early 20th centuries. If the architectural style is unusual for the indicated time of construction, or if the footprint, number of stories, or lot location differ from that shown in the Sanborn maps, or if the address is not reflected in old city directory listings, the building may have been moved on site or the original building demolished or destroyed by fires.
As you spend time looking through city directories, note that address change took place citywide in 1884, 1895, and in the 1870s. Be aware that a building may have three different house numbers due to changes in the numbering system, and that street names have changed over the years.
Other sources to consider are letters, diaries, genealogical records, dateable photographs, account books, and scattered references in periodicals.
An abstract of title transfers ownership of the land, and not the date of construction. But it may provide clues. Look for increases in the consideration, the taxes, or for mortgages, which may indicate construction. Note the names of owners, which are useful when referring to the city directories.
Information about the occupants and/or owners obtained from city directories can often be found in the obituaries of old newspapers on microfilm in the library. Death records for those buried in Elgin are available at the offices of Bluff City Cemetery (ledgers), Lake St. Memorial Park, and on microfilm in the Gail Borden Public Library.
In addition to newspaper obituaries, bound copies of the Elgin National Watch Company's Watch Word magazine accounts of the deceased. Thirty years of this publication are indexed on microfilm and available at the Gail Borden Public Library.