Reference:
http://www.illinoisgreenfleets.org/fuels/index.html

Conversion Rebate Amount: The amount of the Conversion Rebate is for 80% of the cost of the conversion of the vehicle to an alternate fuel up to $4,000.

Application Deadline for a Conversion Rebate: There has been a change in the application deadline for a Conversion Rebate! In 2009, the Alternate Fuels Act was amended by the Illinois General Assembly and signed by the Governor to change the application deadline for a Conversion Rebate. However, this change became effective on August 14, 2009 and only affects vehicle conversions to an alternate fuel that are completed on or after August 14, 2009.

For applicants for a Conversion Rebate, in which the vehicle conversion was completed from January 1, 2009 through August 13, 2009, the application deadline is December 31, 2009 (same deadline as before).

For applicants for a Conversion Rebate, in which the vehicle conversion was completed on or after August 14, 2009, there is now a 12-month application time period (with the deadline being the last day of the 12th month). For example, if the vehicle conversion was completed on August 16, 2009, the application must be postmarked by August 31, 2010.

The Illinois EPA processes Conversion Rebates twice each year, at the end of June and at the end of the year, on a six-month cycle. Your approved Conversion Rebate application will be processed for payment at the end of the next six-month cycle. Please call the Illinois EPA at (800) 635-2380 if you have any questions.

* Please contact your accountant for advice in your situation.

The American Road & Recovery Act of 2009 (also known as the Stimulus bill) includes tax credits for businesses and consumers that have a plug-in conversion performed on their vehicle(s).

...
SEC. 1143. CONVERSION KITS.
(a) IN GENERAL.—Section 30B (relating to alternative motor
vehicle credit) is amended by redesignating subsections (i) and
(j) as subsections (j) and (k), respectively, and by inserting after
subsection (h) the following new subsection:
‘‘(i) PLUG-IN CONVERSION CREDIT.—
‘‘(1) IN GENERAL.—For purposes of subsection (a), the plugin
conversion credit determined under this subsection with
respect to any motor vehicle which is converted to a qualified
plug-in electric drive motor vehicle is 10 percent of so much
of the cost of the converting such vehicle as does not exceed
$40,000.
‘‘(2) QUALIFIED PLUG-IN ELECTRIC DRIVE MOTOR VEHICLE.—
For purposes of this subsection, the term ‘qualified plug-in
electric drive motor vehicle’ means any new qualified plugin
electric drive motor vehicle (as defined in section 30D, determined
without regard to whether such vehicle is made by
a manufacturer or whether the original use of such vehicle
commences with the taxpayer).
‘‘(3) CREDIT ALLOWED IN ADDITION TO OTHER CREDITS.—
The credit allowed under this subsection shall be allowed with
respect to a motor vehicle notwithstanding whether a credit
has been allowed with respect to such motor vehicle under
this section (other than this subsection) in any preceding taxable
year.
‘‘(4) TERMINATION.—This subsection shall not apply to
conversions made after December 31, 2011.’’.
(b) CREDIT TREATED AS PART OF ALTERNATIVE MOTOR VEHICLE
CREDIT.—Section 30B(a) is amended by striking ‘‘and’’ at the end
of paragraph (3), by striking the period at the end of paragraph
(4) and inserting ‘‘, and’’, and by adding at the end the following
new paragraph:
‘‘(5) the plug-in conversion credit determined under subsection
(i).’’.
(c) NO RECAPTURE FOR VEHICLES CONVERTED TO QUALIFIED
PLUG-IN ELECTRIC DRIVE MOTOR VEHICLES.—Paragraph (8) of section
30B(h) is amended by adding at the end the following: ‘‘,
except that no benefit shall be recaptured if such property ceases
to be eligible for such credit by reason of conversion to a qualified
plug-in electric drive motor vehicle.’’.
(d) EFFECTIVE DATE.—The amendments made by this section
shall apply to property placed in service after the date of the
enactment of this Act.


Full information can be found on the IRS website.

AND

PUBLIC LAW 111–5—FEB. 17, 2009

* Please contact your accountant for advice in your situation.

In Colorado, House Bill 1331, the "Incentives for Efficient Motor Vehicles" act, creates or extends tax credits for natural gas conversions, plug-in hybrid conversions, diesel-electric hybrid conversions (don't see many of those) and also supports anti-idling technologies. The credits are maxed out at $6,000 and you can find full details here. H.B. 1331 recently passed the Colorado State House and Senate and was then signed by the Governor.

* Please contact your accountant for advice in your situation.

Alternative Fuels Rebate -- Dealer Information Form DR 0168

Alternative Fuels Rebate -- Government Charitable Organization Application Form DR 0167