Maps
Digital Sanborn maps 1867-1970 offers over 660,000 large-scale fire insurance maps of over 12,000 American towns and cities. Shows locations of individual buildings
City Directories
Most directories have lists of residents with address and occupation, followed by a business directory topically arranged. There are often lists of schools, churches, government agencies, charitable societies, fraternal organizations, etc.
The major online sources are:
Ancestry Library Edition (Most comprehensive)
Tufts Boston City Directories. Other city directories can be found in United States Online Historical Directories
Most city directories are available online, but some are available only on microfiche or microfilm:
American directories through 1860. 6820 microfiches
HOLLIS Record
Guide: Bibliography of American directories through 1860, by Dorothea N. Spear. Worcester, Mass., American Antiquarian Society, 1961, 389 p.
HOLLIS Record
Continued by:
United States city directories. 1861-1881. HOLLIS Record
United States city directories. 1882-1901. HOLLIS Record
United States city directories. 1902-1935. HOLLIS Record
City directories of the United States. 1936-1960 HOLLIS Record
Harvard only has these directories for Boston (1861-1960), Cambridge (1902-1935) and Columbus, Ohio (1861-1901), all of which are available online.
For cities we don’t have use U.S. City Directories on Microfilm in the [Library of Congress] Microform Reading Room (bottom of page) to specify the reel, then Interlibrary Loan.
Additional resources for directories
For rural districts see Landownership Maps and Atlases. Available via Ancestry Library Edition: choose Card Catalog in the Search menu, then under Filter by collection, hit Maps, Atlases and Gazetteers, then North America.