The five top-level IP Registrars (ARIN, RIPE, APNIC, LACNIC, AFRINIC) manage tens of million IPV4 and IPV6 addresses, assigning them to networks around the world. These addresses are key to accessing the Internet for all end-users.
About once a year, I generate the statistics out of the IP address database I maintain. The last one was published back in August 2007,  and, as can be imagined, there have been substantial changes that have occurred in the last 12 months.
At the country level, there has been a substantial change in the top five as China has superseded Japan in the total number of IPV4 addresses. In fact, in the last 12 months, Japan has seen a net loss in the total number of allocated IPV4 addresses.

country NETWORKS IPS
UNITED STATES 33758 1441234432
CHINA 1478 161991424
JAPAN 1971 148897280
EUROPEAN UNION 4766 120292412
UNITED KINGDOM 3460 85509464
GERMANY 2237 78525232
CANADA 5201 73586944
FRANCE 1692 68225984
KOREA, REPUBLIC OF 631 66108928
AUSTRALIA 5950 35859200
ITALY 921 29520320
BRAZIL 266 27657728
TAIWAN, PROVINCE OF CHINA 410 23842816
MEXICO 158 21504000
SPAIN 494 20755104
NETHERLANDS 1319 20614440
RUSSIAN FEDERATION 2654 19910472
SWEDEN 800 16947104
INDIA 542 16661504
SOUTH AFRICA 790 13828352
POLAND 1457 12799116
DENMARK 459 9149792
TURKEY 269 8892096
FINLAND 619 8812672
SWITZERLAND 1217 7642056
ROMANIA 693 7612416
HONG KONG 633 7537408
NORWAY 388 7119648
AUSTRIA 793 6938336
INDONESIA 429 6885376
ARGENTINA 380 6241280
BELGIUM 370 6016640
CZECH REPUBLIC 572 5592704
NEW ZEALAND 1187 5560064
VIETNAM 81 4388352
THAILAND 338 4367104
UKRAINE 1547 4356416
SINGAPORE 395 4352512
CHILE 380 4313344
IRELAND 204 4025760
MALAYSIA 238 3949312
ISRAEL 211 3936192
PORTUGAL 134 3859296
COLOMBIA 217 3818752
GREECE 220 3746816
VENEZUELA 109 3592704
HUNGARY 231 3577472
PHILIPPINES 257 2957056
BULGARIA 331 2923264
UNITED ARAB EMIRATES 23 2278656
EGYPT 85 2255616
SAUDI ARABIA 154 2194176
LITHUANIA 117 1997696
IRAN, ISLAMIC REPUBLIC OF 94 1588224
CROATIA 62 1438048
SLOVAKIA 157 1418240
COSTA RICA 24 1332224
LATVIA 187 1316864
PAKISTAN 110 1302016
PERU 74 1253120
SLOVENIA 187 1210752
PANAMA 51 1038592
ESTONIA 77 1008912

The adjustment in China is completely expected, as China has substantial room to expand its IPV4 population, compared to a country such as Japan which is likely approaching saturation in this area.
In the total number of IPV4 addresses assigned by registrar, ARIN (US, Canada, and parts of the Caribbean) still has a substantially larger population than the other regions. However, this region only grew by 3 million IPV4 addresses in the last 12 months, compared to 42 million for RIPE (Europe and the Middle East), and 74 million for APNIC (Asia-Pacific). LACNIC (Mexico, Latin and South America) grew by 13 million IPV4 addresses and AFRINIC (Africa) by 4 million.

registry NETWORKS IPS
arin 39231 1583464704
ripencc 29996 539874744
apnic 15143 480405504
lacnic 2152 74576896
afrinic 1325 20201216

Some of this growth in APNIC, AFRINIC, and LACNIC can be attributed to adjustments in the Registry structure itself. Now that there are five registrars with responsibility for a clearly defined set of nations, a number of adjustments have had to occur in the registrar of record for IPV4 ranges.
In the past, for nations that were not explicitly covered by a regional registrar, the IPV4 range may have been assigned by the registrar now responsible for the region, most likely ARIN or RIPE.
Now that there are registrars specifically designated to cover these formerly grey areas, these historical artifacts are being corrected as registry information is renewed.
However, this cannot directly account for the noticeable growth in AFRINIC, APNIC, and LACNIC relative to the two older registrars. This is yet another indication of the strong growth of the Internet outside of its established base of the United States, Canada, Western Europe, and a small number of industrialized nations in the Asia-Pacific region.