Publication 542
taxmap/pubs/p542-006.htm#TXMP221ac39fA corporation should keep its records for as long as they may
be needed for the administration of any provision of the Internal Revenue Code.
Usually records that support items of income, deductions, or credits on the
return must be kept for 3 years from the date the return is due or filed,
whichever is later. Keep records that verify the corporation's basis in property
for as long as they are needed to figure the basis of the original or
replacement property.
The corporation should keep copies of all filed returns. They
help in preparing future and amended returns.