There have been 117 Holy years since they were granted in 1122.
In the early Middle Ages the 30 December was St James’ Feast day, based on the old Hispanic (Mozarabic) rite. In the 11th century King Alfonso VI abolished the Hispanic rite in favour of the Roman rite and 25 July became the principal feast day to commemorate the martyrdom of St. James. December 30 was incorporated into the present liturgical calendar as the Feast of the Translation of his relics.
And, just to confuse matters more, although we celebrate his Feast Day on 25th July using the Roman Rite calendar, it was formerly on the 5th August on the Tridentine Rite calendar.
Due to wars and other calamties, some Holy Years were postponed or held in consecutive years.
You can watch a clip of the Holy Year in 1915 here:
http://www.youtube.com/watch?v=NsnB1mLZwlQ
Holy Years - past and future:
1604 1700 1802 1909 2004 2100 2202
1610 1706 1813 1915 2010 2106 2213
1621 1717 1819 1920 2021 2117 2219
1627 1723 1824 1926 2027 2123 2224
1632 1728 1830 1937 2032 2128 2230
1638 1734 1841 1943 2038 2134 2241
1649 1745 1847 1948 2049 2145 2247
1655 1751 1852 1954 2055 2151 2252
1660 1756 1858 1965 2060 2156 2258
1666 1762 1869 1971 2066 2162 2269
1677 1773 1875 1976 2077 2173 2275
1683 1779 1880 1982 2083 2179 2280
1688 1784 1886 1993 2088 2184 2286
1694 1790 1897 1999 2094 2190 2297