CPI index data by year is in Table 24 of the CPI Detailed Report from the U.S. Bureau of Labor Statistics. The Bureau's data begins in 1913.
The CPI data in Table 24 of the Bureau's report, updated monthly, includes historical yearly and monthly data and shows the percentage change each year from the preceding year. The table also provides data on semi-annual averages beginning in 1984.
Organizations such as the Federal Reserve Bank of Minneapolis provide summarized versions of the yearly CPI data for use by educators and the general public, and organizations such as the Social Security Administration provide subsets of the data.