You've looked at alternatives to the Federal Census in the past, i.e. city directories, phone books, newspapers, etc. Why? Because a lot happens between each 10-year period "snap-shot" by the Federal enumerators. Let's look at state census records and even local census records.
States took a census of the population in various years and for various reasons. States used their enumerations for district demographics, taxation, militias, and occasionally for school planning. Because of their independent motivation without familial agenda, genealogists consider these records valuable and trustworthy resources. Generally speaking, state census counts were done mid-way between the 10-year Federal Census, i.e., 1855, 1865, 1875.
State census records are available for 41 states plus the District of Columbia. Some of these records are limited in scope and only include a county or two. Many are territory records, and some are nothing more than a "head count" (just a tally without names), but they can be good information sources. Each state census asked different questions, and the information given often may be found nowhere else.
Some researchers make outlines of the census headings. Having a standard form should help to extract all the information needed for documentation. There are several good forms for the Federal Census that you can find online at Ancestry, Gentrek, and other sites. For state censuses, I use a spreadsheet and generate a template that can be used for that year and location. Always record the research facility or repository, the film number, and the page number in your notes to make it easier to locate and review those records later. It is a good idea to photocopy those records which contain information on your family. Secure a few pages on each side of your family's residence to keep track of their neighbors. Often they are (or later become) in-laws.
Here is a list of the state census records available which contain at least the surname of the head of household:
Seven States had no state census (so don't bother looking): Idaho, Kentucky, Montana, New Hampshire, New Jersey, Pennsylvania, Vermont.
AL - 1818 partial; 1820 territorial; 1821 partial; 1823; 1850; 1855 head of household only; 1866 head of household only; 1907 partial
AK - 1878 Unalaska, Belkofski, Micholayevsk and Protassof; 1879 Sitka Post only; 1881 partial; 1885 partial; 1890-95 partial; 1904 partial; 1905 partial; 1906-07 partial; 1914 Saint Paul and Saint George Islands only; 1917 Saint Paul and Saint George Islands only
AR - 1823 Arkansas Sheriff's Census; 1829 Arkansas Sheriff's Census; 1865 Washington County only; 1911 Census of Confederate Veterans
AZ - 1866 partial; 1867 partial; 1869 partial; 1872 partial; 1874 partial; 1876 partial; 1880 partial; 1882 partial
CA - 1788 partial; 1790 Padron (Spanish Census); 1796 San Carlos Mission Census; 1797-98 San Luis Obispo Mission Census; 1816 Padron of Los Angeles; 1836 Padron of Los Angeles; 1844 Padron of Los Angeles; 1852 complete
CO - 1861; 1866 northeastern Colorado only; 1885
DE - 1782 Ordered by the General Assembly, conducted in January 1782
District of Columbia - 1803; 1867; 1878
FL - 1825 Leon County only; 1855 Marion and Franklin counties; 1866 children ages 5 - 18. Franklin only; 1867 Franklin, Hernando, Madison, Orange, and Santa Rosa only; 1868 Levy County only; 1875 Alachua County only; 1885; 1895 Nassau County only; 1935 partial; 1945 partial
GA - 1798 Greene County only; 1800 Oglethorpe County only; 1810 partial; 1827 Taliferro County only; 1834 partial; 1838 Laurens, Newton, and Tattnall counties only; 1845 partial; 1852 Jasper County and city of Augusta only; 1853 partial; 1859 Columbia and Terrell counties only; 1865 partial; 1879 Columbia County only; 1890 Crude copy of lost 1890 Federal Census
HI - 1878 Oahu, Maui, and Hawaii; 1890; 1896 Honolulu only
IL - 1810 Part of Indiana Territory; 1818 Illinois Territory; 1820 partial; 1825 partial; 1830 partial; 1835 partial; 1840 partial; 1845 partial; 1855 partial; 1865 partial
IN - 1807 Territorial; 1853 partial; 1857 Blackford County only; 1871 Blackford County only; 1877 Blackford and Fayette counties only; 1883 Blackford County only; 1889 Blackford County only; 1901 Washington County only; 1913 Henry County only; 1919 Ripley and Starke counties only; 1931 Henry County only
IA - 1836 Part of Wisconsin Territory; 1838 partial; 1844 Keokuk County only; 1846 Louisa, Polk, and Wapello counties only; 1847 partial; 1849 partial; 1851 partial; 1852 partial; 1854 partial; 1856; 1885; 1895; 1905; 1915; 1925
KS - 1855 List of eligible voters; 1865; 1875; 1885; 1895; 1905; 1915; 1925
LA - 1745 Point Coupee only; 1791 New Orleans only; 1853 partial; 1858 Carrollton only
ME - 1837 Surplus Revenue Census
MD ~ 1776 partial; 1775-78 Constable's Census of Charles County
MA - 1855; 1865
MI - 1837 partial; 1845 partial; 1854; 1864; 1874; 1884; 1888 Special Civil War Veterans Census; 1894; 1904
MN - 1820 Part of Michigan Territory; 1836 Part of Wisconsin Territory; 1838 Part of Wisconsin Territory; 1840 Parts included in Wisconsin and Iowa Territories1849 partial; 1853 partial; 1855 partial; 1857 partial; 1865 partial; 1875; 1885; 1895; 1905
MS - 1792 Natchez District; 1801 partial; 1805 partial; 1808 partial; 1810 Natchez District; 1816 Natchez District; 1818 partial; 1820 partial; 1822 partial; 1823 partial; 1824 partial; 1825 partial; 1830 partial; 1833 partial; 1837 partial; 1840 partial; 1841 partial; 1845 partial; 1850 partial; 1853 partial; 1860 partial; 1866 partial
MO - 1797 New Madrid District; 1803 New Madrid District; 1817 St. Charles District; 1819 St. Charles District; 1840 partial; 1844 partial; 1852 partial; 1860 partial; 1864 partial; 1876 partial; 1880 partial
NE - 1854 Territorial; 1855 partial; 1856 partial; 1865 Otoe and Cuming counties only; 1869 Butler and Stanton counties only; 1885
NJ - 1855 partial; 1865 partial; 1875 partial; 1885; 1895; 1905; 1915
NM - 1790 Spanish Colonial Census; 1823 Mexican Census; 1845 Mexican Census; 1847 Taos; 1855 Tecolote; 1885; 1891 Santa Fe; 1918 Belen; 1928 Los Lunas
NY - 1790 Albany County only; 1825 partial; 1835; 1845; 1855; 1865; 1875; 1890 New York City Policeman's Census; 1892; 1905; 1915; 1925
NC - 1784; 1785;1786 partial; 1787
ND - 1857 Pembina County only; 1885 partial; 1915; 1925
NV - 1862-63 Territorial; 1875
OH - 1800 Part of the Northwest Territory; 1801 Clermont County only; 1803; 1807; 1811 Ashtabula County only; 1819 Shelby, Clermont, and Ashtabula only; 1823 Shelby and Ashtabula only; 1827 Allen, Miami, and Shelby counties only; 1831 Fairfield, Portage, and Shelby counties only; 1835 Ashtabula, Miami, Shelby, and Portage counties only; 1839 Fairfield and Portage counties only; 1843 Mercer, Shelby, and Ashtabula counties only; 1847 Auglaize, Mercer, Logan, Shelby, and Perry counties only
OK - 1890 Special Territorial Census; 1907 partial
OR - 1842 partial; 1843 partial; 1845 partial; 1849 partial; 1850 partial; 1853 partial; 1854 partial; 1855 partial; 1856 partial; 1857 partial; 1858 partial; 1859 partial; 1865 partial; 1870 partial; 1875; 1885 partial; 1895; 1905
RI - 1774 Colonial Census; 1777 Military Census; 1782 partial; 1865; 1875; 1885; 1905; 1915; 1925; 1935
SC - 1825 partial; 1829 Fairfield and Laurens Districts; 1839 Kershaw and Chesterfield Districts; 1869 partial; 1875 partial
SD - 1885 partial; 1895 partial; 1905; 1915; 1925; 1935; 1945
TN - 1891 Male inhabitants only, 21 years of age and upward
TX - 1829-1836 Mexican Censuses; 1840 Tax List; 1846 Poll Lists
UT - 1852 Index to Bishops Report; 1856 Territorial Census
VA - 1782 partial; 1783 partial; 1784 partial; 1785 partial; 1876 partial
WA - 1856 partial; 1857 partial; 1858 partial; 1860 partial; 1871 partial; 1874 partial; 1877 partial; 1878 partial; 1879 partial; 1880 partial; 1881 partial; 1883 partial; 1885 partial; 1887 partial; 1889 partial; 1891 partial; 1892 partial; 1898 partial
WV - many of the early years are included with Virginia
WI - 1836; 1838 partial; 1842; 1846 partial; 1847 partial; 1855 partial; 1865 partial; 1875; 1885; 1895; 1905
WY - 1875 city of Cheyenne only; 1878 city of Cheyenne only
Notice many of the years listed above are labeled "partial." Partial indicates an incomplete census. Some state census contain only a county or two. Always check with state genealogy societies, historical societies, or state archives to learn what records are extant.
To research most state censuses, plan ahead in order to avoid unnecessarily reading the microfilms for an entire state. Most state census are not indexed, but volunteers have indexed many individual counties. So always check for a possible index. state census records are normally sorted by county name.
Where To Find the State Censuses
You can view state censuses at local family history centers, historical societies, state archives, genealogy societies and similar research libraries. Phone ahead to verify the facility has the information you may need to research.
Websites with state census images are few and incomplete. As more volunteers participate in transcription, more images will become available. A periodic scan for them takes only a few seconds and may reveal just the information you seek. I use Copernic Search Agent, which allows you to save and update your searches, and it quickly uncovers any new listings.
Besides state census records, you may find other local records valuable resources. Some other sources include the following:
Church membership; land grants; lodge membership; plat maps; school census; settlers census; tax lists (income, personal, poll, real estate, etc.); union membership; and voter registration.
Whenever researching any geographic area, remember to inquire of each repository if there are other records available that might list your ancestors. Often curators and librarians know sources to help you find a missing ancestor. When they do, show them your gratitude -- to encourage them to do it again!