Works by Niernsee or by the firm (with attribution) are: • Grace Episcopal (later called
Grace and St. Peter's Church) Park Avenue & West Monument Street, 1850–52 designed with Nielsen • Emmanuel Episcopal Cathedral at Eager St, 1857, designed with Nielsen • The
Green Mount Cemetery hilltop chapel, on Greenmount Avenue,
Baltimore, Maryland, which he designed with Nielsen, is a
Gothic Revival work. • Baltimore's
Johns Hopkins Hospital at 500 Broadway, and the
Johns Hopkins Colored Children Orphan Asylum. • 1855–56:
St. John the Evangelist Roman Catholic Church (by Niernsee & Neilson), Baltimore. Listed on the
National Register of Historic Places (NRHP) in 1982. • 1855:
Saint Paul's Church, 102 North Union Street,
Petersburg, Virginia (Niernsee & Neilson), NRHP-listed. • c. 1855,
Villa Anneslie (mansion), 529 Dunkirk Road,
Towson, Maryland (Niernsee, John Rudolph), NRHP-listed. • 1856-1865,
Baltimore and Ohio Railroad Camden Street Station, 301 West Camden Street,
Baltimore, Maryland (Niernsee & Neilson) • 1868:
Aigburth Vale (mansion) in Towson (by Niernsee & Neilson), listed on the
National Register of Historic Places (NRHP) in 1999. • 1870:
Churchville Presbyterian Church (Italianate clock tower by Niernsee & Neilson),
Churchville, Maryland, listed on the NRHP in 1986. Not in date order: •
Church of the Most Holy Trinity, 720 Telfair Street,
Augusta, Georgia (Niernsee, John Rudolph), NRHP-listed • St. Mary's Catholic Church (1858) located in the
Edgefield Historic District, located along both sides of
U.S. Route 25 through the town of
Edgefield, South Carolina (Niernsee, John R.), NRHP-listed. •
Emmanuel Church,
U.S. Route 301,
Port Conway, Virginia. (Niernsee & Neilson), NRHP-listed/ •
Martin's Brandon Church, Virginia Highways 10 and 1201,
Burrowsville. (Niernsee & Neilson), NRHP-listed. •
Mount Vernon Place United Methodist Church and Asbury House, 2–10 East Mount Vernon Place/East Monument Street (at North Charles Street/Washington Place-North), Baltimore, (Niernsee & Neilson), NRHP-listed. ==Personal life==